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UNITED STATES DEPARTMENT OF THE INTERIOR

TITANIUM DEPOSITS OF

NELSON AND AMHERST COUNTIES

VIRGINIA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 198

UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Professional Paper 198

OCCURRENCE AND ORIGIN OF THE TITANIUM DEPOSITS

OF NELSON AND AMHERST COUNTIES, VIRGINIA

BY

CLARENCE S. ROSS

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON: 1941

For sale by the Superintendent of Documents, Washington, D. C. - - Price 25 cents (Paper cover)

CONTENTS

Abstract.-------------- .____________ .

Introduction._______________ __________

General geology-______________________

Petrography. _________________________

Quartz monzonite____ _____ ________

Roseland anorthosite____. __________

Primary andesine anorthosite ____

Granulated andesine anorthosite. 

Oligoclase anorthosite__________

Border facies._________________

Pegmatitic and aplite zones _____

Ferromagnesian rocks________--_ _ _ _

Quartz lenses______________________

Nelsonite_ ________________________

Definition _____________________

Distribution and occurrence_____

Ilmenite nelsonite______________

Rutile nelsonite_-______________

Mineralogy..__________________________

Antiperthitic andesine ______________

Microcline. _______________________

Rutilated quartz___________________

Clinohypersthene_. ________________

Clinozoisite _______________________

Amphiboles _______________________

Micas__________________________

Rutile _________ .---____--_________

Ilmenite._________________________

Sphene (leucoxene)________________

Magnetite- _-_-__-___-__-_-_______

Apatite ___________________________

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Mineralogy—Continued. 

Minor minerals _____

Origin of the rocks and minerals._. ___________________

Andesine anorthosite____________________________

Oligoclase anorthosite________-_-____--_----_-___

Quartz lenses___________________________________

Border facies___________________________________

Ferromagnesian dikes-______-___-_---_-_____-__-

Disseminated minerals._._________ ___________

Ferromagnesian lenses.__________________________

Nelsonite ____________________-----__-_-_--_-_-_

Summary of evidence of origin.__________________

Related titanium deposits...-_________-----_-________

St. Urbain, Quebec_.___________--_--__--___.__

Magnet Cove, Arkansas.________________________

Physicochemical processes controlling mineralization____.

Theoretical background..________________________

Stability of minerals.______________----_--__

Reaction principle._____________________ ...

Relation between alkalies and alumina. _______

Physical character of replacing solutions___.___ 

Source of ferromagnesian materials____________

Chemistry of replacement..._____________________

Source and character of the solutions._____________

Mode of segregation and transportation of mineralizing materials. _______________________________

Phosphorus.________________---_---__---_-_

Titanium. __________-______-____------_---_

Iron, magnesium, and calcium_.______________

Restatement of paragenesis______________________

Index _______.______________-_______----.---___-_--

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59

ILLUSTRATIONS

PLATE 1.

2.

3.

4.

5.

6, 7, 8. 

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19. 

FIGURE 1

Page 

Relation of partly granulated feldspar to rutile.__,-__-_-____----_________________________----------_--__ 40

Replacement of feldspar by secondary minerals._________________________________________________________ 41

A, B, Secondary minerals replacing feldspar; C, Antiperthite; D, Perthite.__________________________________ 42

Secondary minerals in feldspar.___-_____________--_-_-____-_-___________________________---_---_--____ 43

A, Rutile in quartz; B, Actinolite replacing quartz; C, Replacement of feldspar by secondary minerals; D, Replacement of feldspar by rutile______________________________________________ ____________________________ 44

Replacement of anorthosite by ferromagnesian minerals,_____________-_____________________------_---_--- 45-47

Replacement of clinohypersthene by hornblende and by apatite. __________________________________________ 48

Augen injection gneiss in schist and its alteration products.._____-_________________ _________-__-___..__.-__ 49

Replacement of anorthosite by nelsonite______________________________________________________________ 50

A, Replacement of anorthosite by nelsonite; B, Replacement of quartz by apatite.__________________________ 51

Amphibolite nelsonite replacing anorthosite and development of schist structure..____________________________ 52

A, B, C, Relation between ilmenite and apatite in nelsonite, C showing residual areas of anorthosite; D,

Clinohypersthene invaded by ilmenite-__•__________________-_____-_-____-_-___-__--___--__----_----- 53

Replacement of anorthosite by nelsonite___ .____________________________________________-_--_------_---- 54

A, Rutile and secondary minerals replacing anorthosite; B, Mineralized anorthosite injection gneiss_____ _______ 55

A, B, C, Quartz and ilmenite replacing clinohypersthene; D, Veinlets of ilmenite in apatite ______ ______________ 56

A, B, Replacement of rutile by ilmenite; C, D, Apatite cut by veinlets of biotite and ilmenite_________________ 57

A, B, C, Replacement of rutile by sphene; D, Replacement of rutile by ilmenite and sphene_____---------_---_ 58

. Map of the Virginia titanium region._______________________________-___---__---_---_-__-----_-------- 2

INSERT

Paragenesis of minerals from the Roseland titanium district, Virginia.

nr

Page 

22

OCCURRENCE AND ORIGIN OF THE TITANIUM DEPOSITS OF NELSON

AND AMHERST COUNTIES, VIRGINIA

By CLARENCE S. Ross

ABSTRACT

The titanium deposits in the central part of Virginia, near the 

eastern base of the Blue Ridge, have long been the world's 

principal source of rutile and contain large supplies of ilmenite. 

The ores are associated with the Roseland anorthosite, a rock 

composed of antiperthitic andesine. This feldspathic rock mass 

is roughly elliptical in shape, covers an area of about 22 square 

miles, and intrudes a gneissic quartz monzonite that forms the 

dominant country rock of the region. The anorthosite shows 

crushing and granulation throughout the area, and only locally 

are there uncrushed residual masses, rarely more than 1 foot in 

diameter, of the coarse-grained primary feldspar. This clastic 

structure is similar to that in other anorthosite masses.

The titanium minerals occur in deposits of two distinct types— 

as disseminated deposits in the anorthosite and as veinlike or 

dikelike masses of a rock known as nelsonite, which is characterized by rutile and apatite or by ilmenite and apatite. Most of 

these masses are within the anorthosite, but a few are outside of 

it. Associated with the anorthosite are a few intrusive dikes and 

numerous ferromagnesian lenses that have replaced anorthosite 

along shear zones. The dikes are evidently offshoots of a deepseated intrusive mass, which is probably a ferromagnesian differentiate of the same primary magma whose other fraction is 

represented by the anorthosite.

The titanium minerals in both disseminated deposits and nelsonites were introduced after the granulation and consolidation 

of the anorthosite and are absent in the primary uncrushed feldspar. They are most abundant in the vicinity of shear zones, 

which evidently acted as feeding channels, and are associated 

with amphiboles, micas, clinozoisite, and quartz, which have 

replaced feldspar. The titanium and associated minerals are 

evidently the result of replacement and not of magmatic segregation or of pyrogenic processes.

The simple mineralogy of the feldspar rock that has been partly 

replaced and the small number of introduced elements present an 

unusually simple problem in the chemistry of replacement, and it 

has been possible to deduce chemical equations that are believed 

to represent closely the chemical processes in the different zones 

of mineralization. In the innermost zone TiOz, FeO, and MgO 

were the essential components introduced. In the next zone 

FeO was deficient, and TiOz and MgO were introduced. The 

outermost zone is characterized by the alteration of feldspar to 

clinozoisite and muscovite, but this has taken place without 

essential changes in the chemical composition of the replaced 

rock.

The geologic and mineralogic relations in the Roseland district 

show that Ti02 , FeO, MgO, and at most small amounts of CaO 

and K2 0 were introduced by invading solutions in the order of 

succession listed. The acid radicals that accompanied these were 

PsOs, F, and a little COa and Cl. An interpretation of this 

sequence in the light of physicochemical laws seems to indicate 

that the P205 and F of apatite (the earliest mineral of the group) 

were segregated from the parent magma by a distillation. CaO

may not have been an essential part of this vapor phase but was 

derived largely from local supplies in calcic feldspar.

At a slightly later stage Ti02 was distilled over as a vf.oor 

phase of titanium tetrafluoride. The ferrous iron of ilmenite 

was in part derived from local ferromagnesian minerals, but part 

of it escaped from the parental ferromagnesian rock as a liquidphase hydrothermal solution, possibly as ferrous halogens or 

bicarbonate. This affords a method for the segregation and the 

sequence of Ti02 and FeO and explains how a high concentration 

of titanium may be derived from a normal ferromagnesian rock 

in which iron is dominant over titanium. The magnesium of the 

ferromagnesian silicates and the calcium of sparse calcite vrere 

probably segregated by the same process as the ferrous iron.

The minerals of the anorthosite and the secondary minerals 

formed by its replacement are described.

INTRODUCTION

The titanium deposits of the Roseland distr'ot, 

Nelson and Amherst Counties, have long supplied most 

of the rutile used in the world, and the district also 

contains important deposits of ilmenite. These deposits 

show two modes of occurrence—one as disseminations 

in a feldspar rock and the other as lenticular veins or 

irregular dikelike bodies, which commonly cut this same 

rock. This paper describes these titanium deposits and 

the rocks associated with them and discusses their 

par agenesis.

Statistics are not available on the production of 

rutile in this country but in 1937 the production \ras 

estimated to be about 2,000 tons, the greater part of 

which came from the Roseland district, in which the 

American Rutile Co. is the only producer. Recently 

the Hot Springs district of Arkansas has begun to 

produce. Norway has long been the only other producing country, and its yearly output has commonly 

been less than 100 tons, but Brazil is now export-ng 

rutile. Only a few of the large bodies of ilmenite in the 

Roseland district have been systematically developed, 

and in the past most of the production has been ir°idental to the recovery of rutile. The Southern Mineral 

Products Corporation is now mining ilmenite from one 

of the larger ilmenite bodies, and the material is bemg 

used in the manufacture of titanium pigments.

The titanium deposits of Virginia have been described 

by Watson and Taber 1 in an excellent report, which

i Watson, T. L., and Taber, Stephen, Geology of the titanium aiid apatite deposits 

of Virginia: Virginia Geol. Survey Bull. III-A, p. 308,1913.

1
TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

should be consulted by those interested in the general 

geology of the region or a detailed description of the 

occurrences; and that report has been a great help in 

the preparation of this paper. The present study has 

been made possible largely through the courtesy of the 

American Rutile Co., especially of Mr. J. H. Morley, 

mining engineer in charge of operations, and the officials 

of the Southern Mineral Products Corporation.

The Roseland district lies in the Piedmont region of 

Virginia, where it merges into the foothill region of the 

Blue Ridge. (See fig. 1.) The area is about equally

FIGURE 1.—Map of the Virginia titanium region. Ruled area shows position of 

anorthosite body.

distant from Charlottesville and Lynchburg, Va., and 

is crossed by the main highway between those cities. 

The main line of the Southern Railway is 5 to 7 miles 

to the southeast, and the nearest stations on that line 

are Arrington and Tye River. The area is drained by 

the Piney and Tye Rivers, which join the James River 

about 12 miles southeast of Roseland. The altitude of 

the immediate region ranges from about 700 feet on the 

Tye River to about 1,200 feet near the northeast part 

of the area, and the average altitude is about 800 feet. 

The crest of the Blue Ridge lies about 12 miles to the 

northwest, but the highest peaks of the region are about 

6 miles east of the main ridge and rise to a height of

about 4,000 feet. These outlying peaks are composed 

of a highly resistant gneissic quartz monzonite.

GENERAL GEOLOGY

The geologic setting of this part of Virginia has been 

described by Watson and Taber 2 and need be outlined 

only briefly. The prevailing rocks of the region are 

gneisses and schists of pre-Cambrian age. The dominant rock of the Roseland district has been named the 

Lovingston granite gneiss, although described on the 

State geologic map 3 as a biotite-quartz monzonite augen 

gneiss. It is part of a zone of intrusive rocks that 

extends from the vicinity of Warrenton on the northeast 

to Roanoke on the southwest, a distance of nearly 200 

miles. The highest peaks of the adjacent parts of the 

Blue Ridge and rugged hill areas of the nearby Piedmont region are formed by this rock.

Locally a fine-grained gneissic or schistose rock, 

which is evidently a metamorphosed sedimentary material, is present. It commonly contain? augenlike 

lenses of microcline. (See pi. 10.) The pre-Cambrian 

geology of this part of Virginia presents many difficult 

and still unsolved problems, and the affiliations of this 

fine-grained gneiss or schist have not been determined. 

It may represent local lenses of the Lynchburg gneiss, or 

perhaps more probably of some other high^ metamorphosed sedimentary rock. The main body of the Lynchburg gneiss lies east of the quartz monzonite (Lovingston granite gneiss), and no part of it has been definitely 

traced into the Roseland district.

The so-called Lovingston granite gneiss is a rather 

variable rock but is in general best described as a 

gneissic, biotite-rich quartz monzonite and will be 

referred to as the quartz monzonite in this paper. 

The igneous character has not been greatly modified 

during the development of the gneissic structure. 

The most marked alteration observed has been along 

the border of the Roseland anorthosite, where it has 

been intruded by feldspathic material.

The quartz monzonite was intruded by a feldspar 

rock here called the Roseland anorthosite. This rock 

is also believed to be pre-Cambrian in age, although 

distinctly younger than the rocks it intrudes. The 

length of this intrusive mass is about 13 miles, the 

greatest width about 1% miles, and the total area about 

22 square miles. The elongation is to the southwest 

and coincides with the general structure of the region. 

A large inlier of quartz monzonite occurs near the northeast end of the intrusion and is marked by Mars 

Mountain, which rises several hundred feet above the 

surrounding area of anorthosite. The bourdary of the 

anorthosite as mapped by Watson and Taber (see fig. 

1) is only approximate in places, owing to concealment 

by a deep mantle of residual soil or to a broad transi2 Idem, pp. 5H-50.

3 Geologic map of Virginia, Virginia Geol, Survey, 1923.
PETROGRAPHY

tional zone between the anorthosite and the enclosing 

rocks.

The Eoseland anorthosite is cut by numerous quartz 

veins, dikes rich in ferromagnesian minerals, and large 

lenticular bodies of a rock called nelsonite.

The Eoseland district lies in a region of very deep 

weathering, and except in areas of rugged relief the 

rocks are weathered to depth of 30 feet or more. 

Good outcrops are observable only along the streams 

and in a few places where they have been exposed by 

mining operations. The Eoselaiid anorthosite has 

weathered more readily than the enclosing quartz 

monozonite. Consequently the anorthosite has been 

reduced to a nearly plane surface, somewhat dissected 

as a result of recent uplift, whereas the more resistant 

quartz monzonite tends to form rugged hills that range 

from a few hundred to more than 1,000 feet in height 

in the foothill region and attain a height of 4,000 feet 

in the Blue Eidge. The nearly pure feldspathic rock 

weathers to a kaolinitic soil, which may be nearly white 

a few feet below the surface; but its iron-rich zones 

and the enclosing schists and gneisses weather into a

red soil.

PETROGRAPHY

QUARTZ MONZONITE

In the course of this investigation the quartz monzonite has been studied only where closely associated 

with the titanium ore deposits. For that reason its 

general character can be best presented by quoting 

from the description given by Watson and Taber: 4

The outside or country rock of the rutile-ilmenite-apatite area 

is a pronounced foliated, quartz-biotite gneiss, which shows in 

many places a considerable development of schists of variant 

composition. Gneiss is the dominant type in this complex of 

metamorphic rocks and has wide general distribution beyond the 

limits of the area mapped throughout the Blue Ridge region of 

central western Virginia. * * * The gneiss has a pronounced 

banded or schistose structure and exhibits considerable textural 

and mineralogical variations, but the prevailing kind is a medium 

to dark-gray rock varying from a fine to medium-coarse, evengranular to porphyritic texture, the rock having in the latter 

case a distinct augen-gneiss appearance. * * * The principal minerals recognizable with the naked eye are feldspar, 

quartz, and biotite. Ilmenite and muscovite and rarely hornblende are also apparent in some specimens. Ilmenite is frequently concentrated in the sands derived from the decay of the 

gneiss. Some of the black grains composing the sand are magnetic and are probably magnetite. Biotite is frequently altered 

to chlorite, and in the vicinity of the gneiss-syenite contact 

much of the quartz in the gneiss is pale blue in color, resembling 

that of the syenite.

Near the contacts with the anorthosite the quartz 

monzonite shows varying degrees of alteration and 

introduction of secondary minerals. The most conspicuous of these minerals is blue rutilated quartz, but 

titanium minerals, and especially sphene have also been 

introduced. Along the borders, especially near Rose 

Mills, there is a wide transitional zone between quartz

4 Watsoa, T. L., and Taber, Stephen, op. cit., p. 201.

monzonite and anorthosite, described in detail on 

pages 4 and 5.

ROSEIAND ANORTHOSITE

The Eoseland anorthosite was called pegmatite by 

Merrill.5 Watson and Taber 6 described it as a syenite, 

although they point out that the dominant feldspar is 

plagioclase (andesine) rather than a potash feldspar 

and suggest, in a footnote, that perhaps anorthosite 

would be an appropriate name.7 On the geologic map 

of Virginia the anorthosite is mapped as albitite. 

Syenite is not a suitable name, as potassium feldspar 

is subordinate to plagioclase. The rock was originally 

made up of very coarse feldspar crystals (see p] .1), 

but granulation has given it a marked variation in 

texture. The rock originally had a pegmatitic habit, 

if "pegmatitic" is used only to describe an unusually 

coarse-grained rock. However, it has not the dikelike 

form of many pegmatites, its granulation has destroyed the coarseness of gram in much of the area, 

and the suggestion that it has genetic affinity with 

anorthosites rather than with normal pegmatites seems 

strong. The Eoseland anorthosite seems to have been 

intruded in the same manner as the anorthosites of 

the Adirondack region of New York. Very marked 

coarseness of grain, partial granulation, antiperthitic 

feldspars, and associated titanium minerals characterize many anorthosites. This feldspar rock of the 

Roseland district is therefore designated anorthosite 

in this paper, although it is somewhat more sodic than 

many anorthosites.

The similarity of the Eoseland anorthosite to anorthosites from other localities has been pointed out by 

Watson and Taber 8 and by Bowen and Buddington,9 

who are both familiar with the anorthosites of the 

Canadian Shield region.

PRIMARY ANDESIHE ANORTHOSITE

The primary rock of the andesine facies of the anorthosite is represented by the ungranulated arer.s of 

feldspar that may be observed in many outcrops, but 

it was best studied in the open-cut mine of the American 

Eutile Co., near Roseland, but later mining operations 

have removed the best of this material. Here the 

primary feldspar forms light bluish-gray ungranulated 

residual areas, as distinguished from the nearly white 

granulated feldspar. These residual areas are as nuch 

as 10 to 20 centimeters in diameter and were evidently 

even larger before partial granulation. The relations 

between the primary feldspar masses and the granulated parts are shown in plate 1. When exanined 

closely the primary andesine shows a satiny appearance, 

owing to the presence of minute lenses of microcline.

s Merrill, G. I'., Eulile mining in Virginia: Eng. and Min. Jour., vol. 78, p. 35, 

1902.

e Watson, T. L., and Taber, Stephen, op. cit., pp. 08-90 

' Idem, p. 79 

8 Idem, p. 

» Bowen, N. L., and Buddington, A. F., personal communications.
TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

The andesine with its intergrown microcline (see pi. 

3, (?) appears to have been almost the only primary 

mineral present in the original rock. This ungranulated primary feldspar is nearly free from secondary 

minerals, which have formed only locally along shear 

fractures that cut across many of the residual masses, 

as shown in plates 1 and 2. An analysis of a sample of 

primary feldspar (p. 10) shows that it is composed of 

about 25 percent of microcline, 51 percent of the albite, 

and 24 percent of the anorthite molecules. A recalculation of the plagioclase indicates that it has a composition of Ab68 . 5 .

GRANULATED ANDESINE ANORTHOSITE

All parts of the ariorthosite mass show crushing and 

granulation, so that millimeter-sized grains, though 

irregularly distributed, make up a large portion of the 

rock. There appear to have been distinct zones of 

maximum crushing, so that areas of almost complete 

granulation alternate with very irregular areas where 

the rock has been fractured but less thoroughly granulated.

The granulated parts of the anorthosite are nearly 

pure white, except where darkened by the introduction 

of clouds of secondary minerals, as shown in plate 2, A. 

However, the abundance of these secondary minerals 

cannot be judged in the hand specimen, as large amounts 

of tremolite, muscovite, and clinozoisite have commonly 

developed in rocks that are white and have remained 

fresh in general appearance. The microscope shows 

an aggregate of feldspar grains that are extremely 

irregular in size, as in a single slide they may range 

from 0.01 to 1.5 or 2 millimeters in diameter. (See 

pi. 2, D.} They are also irregular and ragged in outline, 

and all but the smallest grams show evidence of strain 

by the presence of undulatory extinction. Commonly, 

ungranulated feldspar shows marked strain on the 

contact with granulated material. (See pi. 2, Z>.) 

Most of the grains show the same type of antiperthitic 

inclusions of microcline as the primary ungranulated 

feldspar, described in the previous section. Only an 

occasional gram and rare border areas on other grains 

are without antiperthitic inclusions.

The granulated feldspar is in general andesine of the 

composition Ab64 to Ab70 , but a small proportion is 

oligoclase, or albite as high as Ab93 . Some rare disseminated grains of albitic plagioclase are free from 

antiperthitic intergrowths and probably represent 

primary crystallization of a late alkalic magma residue; 

however, the presence of antiperthite in most of the 

albite grains indicates albitization of earlier andesine.

A very small amount of quartz fills interspaces between some of the feldspar grams. It is free from the 

inclusions of rutile needles that characterize the bluegray quartz associated with the replacing lenses of 

ferromagnesian minerals. Most analyses of andesine 

anorthosite show a small percentage of normative quartz

as shown by the analyses given by Watson ard Taber. 10 

A very few small grains of limpid potassium feldspar 

are also present in the andesine anorthosite, and evidently belong to the same stage in the formation of that 

rock as the interstitial quartz. No part of the granulated anorthosite seems to be entirely free from secondary minerals, and hi much of the rock they are very 

abundant. These minerals are rutile, ilmenite, sphene, 

biotite, muscovite, actinolite, tremolite, and clinozoisite. 

In a few specimens they occur as small lenses or veinlets, but in general they form swarms of microscopic size 

within feldspar grams.

OLIOOCLASE ANORTHOSITE

The tunnels of the American Rutile Co., 1 ave penetrated a mass of gray, nearly equigranular oligoclase 

anorthosite which locally borders the andesine anorthosite. The individual mineral grains average about 0.5 

millimeter in diameter, but the grain of the rock appears to be coarser because light and dark minerals are 

grouped in aggregates 2 to 3 millimeters in diameter.

A microscopic study shows that the rock is composed 

largely of antiperthitic oligoclase (Ab80 ), vhich has 

been partly replaced by secondary minerals, as described on page 17. Small amounts of rutile-free 

quartz and potassium feldspar form filmlike areas 

around oligoclase, as described on page 10. Secondary 

mineralization has altered primary pyroxenes to amphiboles and introduced abundant rutilated blue quartz, 

micas, and clinozoisite. This rock is more sodic than 

the andesine phase, but the associated minerals and 

their relations are similar, and the rock appears to have 

been composed originally of antiperthitic feldspar and 

pyroxenes.

BORDER PACIES

The contact between the anorthosite and the enclosing rock is commonly marked by an injection gneiss 

formed by the introduction of feldspathic material along 

schist planes. The best example of this contact is on 

the southeast border near Rose Mills, where a transitional zone about 500 feet wide is well exposed in the 

bed of Alien Creek and in a gully near the roadside. 

The transitional facies is a gneissoid zone, irade up of 

anorthosite lenses that parallel the schistosity and 

alternate with other lenses almost free from anorthosite. These anorthosite lenses become progressively 

fewer and narrower with increasing distance from the 

contact.

The lenses of anorthosite in the gneissic rock range 

from mere stringers to lenses several feet across. In 

the hand specimen they show a feldspar matrix that 

contains large but variable amounts of secondary 

minerals. (See pi. 16, B.) These are arranged in roughly 

parallel lenses that coincide with the schistorHy of the 

enclosing schist and give the rock a roughK gneissic 

structure. These secondary minerals are dark-colored

'° Watson, T. L., and Taber, Stephen, op. cit., p. 78.
PETROGRAPHY

silicates, blue quartz, rutile, and a little ilmenite. 

Microscopic study shows that the feldspar is largely 

oligoclase that has a composition of about Ab8o and so 

is slightly more sodic than the anclesine of the main 

mass of the anorthosite. In some lenses this is largely 

antiperthitic, but in others a large proportion is free 

from antiperthitic microcline. This part is in general 

much less replaced by secondary silicates than the 

an tiperthitic material. The fresher type of feldspar is 

surrounded by a narrow reaction rim of microcline.

The blue quartz forms grains 3 centimeters hi maximum length that tend to be elongated in the direction of 

gneissic structure (see pi. 16, B). They have rounded 

borders but are markedly lobate in outline. Some 

lenses of anorthosite contain irregular lenses of material 

which was originally clinohypersthene that formed 

along shear zones This material is now completely 

altered to a fibrous hornblende aggregate. Swarms of 

secondary silicates have formed abundantly in the feldspar. These commonly fill most of an antiperthitic 

feldspar grain, but elsewhere they are localized along 

fractures in feldspar. The order of formation of minerals is as follows: Antiperthitic feldspar, perthite-free 

plagioclase, reaction rim of microcline, clinohypersthene, quartz, apatite, rutile, ilmenite, and the disseminated hornblende, sericite, biotite, and clinozoisite. 

The relation of quartz to clinohypersthene is not evident, and the disseminated minerals evidently formed 

together. Calcite appears to have been the last mineral 

to be formed.

The lenses of schist or gneiss that alternate with 

anorthosite are all indurated and much more resistant 

to erosion than the normal rocks of the immediate area. 

A microscopic study indicates that the material was 

originally a quartz schist with lesser amounts of microcline, oligoclase, and biotite. Feldspar lenses or augen 

of microscopic size, related to the anorthosite, have been 

introduced into this material, and this was followed by 

the introduction of secondary minerals. Some lenses 

are largely quartz with secondary biotite; others show 

zones of almost pure epidote. In general, the schist 

lenses are made up of partly recrystallized primary 

schist material, introduced feldspar, and secondary 

biotite, epidote, clinozoisite, actinolite, ilmenite, leucoxene, and more rarely garnet. One specimen from the 

same locality appears to be a lens of quartz monzonite, 

rather than quartz schist.

A specimen of injection gneiss was obtained near the 

contact with the north border of the anorthosite mass, 

which is exposed about 1 mile southeast of Massies 

Mill and again in a road cut a few rods east of the Massies 

Mill School. (See pi. 10.) This material has intruded a local mass of fine-grained schistose rock that 

is evidently metamorphosed sedimentary material. 

Mrs. Anna J. Stose u reports that such schistose lenses

11 Personal communication.

are commonly intruded by microcline augen gneirs in 

adjacent parts of Virginia, and so this injection gneiss 

is probably older than the material at Rose Mills and 

the nearby aplitic lenses. However, it has beer replaced by secondary minerals similar to those at Rose 

Mills. A microscopic examination of the injectionfree fine-grained schist shown at the left of plate 10 

shows that it is composed of about equal parts of quartz, 

feldspar (largely microcline), and biotite. It also contains small amounts of amphiboles, clinozoisite, and 

sphene. These have also formed in the intrusive feldspar lenses and so are later than the primary schist 

material.

This fine-grained schist material was intruded by 

feldspathic material, and most of the specimen is an 

injection gneiss composed of large, nearly white feldspar augen enclosed in dark contorted schist material 

that bends around them. The augen are dominantly 

microcline but contain oligoclase as disseminated grains 

and perthitic lenses. The microcluie has been partly 

replaced by large areas of coarse-grained myrmekite, a 

plumose intergrowth of quartz and oligoclase.

Subsequent to the introduction of the microcline the 

rock was sheared, producing schistose zones, which cut 

across or more commonly bend around the microcline 

augen. Diagonal fractures were also developed within 

the microcline areas and make an angle of about 45° 

with the prevailing direction of schistosity, and minor 

amounts of secondary minerals were formed along these 

fractures. The augen gneiss now contains two distinct 

types of schistose material. One is the original schist 

that has been distorted and recrystallized during the 

introduction of the microcline, and the other is a product 

of later shearing and alteration of both microcline and 

schist. In plate 10 the older schist shows as darkcolored areas. The areas of later shearing are light 

gray, and many of them cut through a single feldspar 

grain. The later schistose areas (those that appear 1'ght 

gray) are composed almost exclusively of muscovite, 

formed mainly by the shearing and alteration of feldspar 

but to a lesser degree by shearing of areas of the older 

schist. The plagioclase of the disseminated grains, the 

myrmekite, and the perthitic lenses has all been replaced by an aggregate of clinozoisite and sericite, 

leaving the microcline nearly fresh. Ilmenite, sphene, 

very finely disseminated rutile, apatite, and blue quartz 

were introduced along these shear zones. The late 

introduction of ilmenite and sphene is shown by the 

absence of fracturing in these minerals, despite the 

extensive shearing the rock has undergone. Apatite is 

very slightly broken but shows no evidence of grp.nulation. The augenlike areas of blue quartz have bQ-en 

strained and slightly sheared but are not granulated. 

The ilmenite has been almost completely altered to 

leucoxene in some areas, but in others only narrow f 1ms 

of leucoxene have formed.
6 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

PEGMATITIC AND APLITE ZONES

The anorthosite is cut by small narrow lenses whose 

minerals seem to be allied to pegmatites, and aplites. 

Pegmatitic material is shown in a quarry operated by 

Dominion Minerals, Inc., on the Piney River about a 

mile northwest of the point at. which the Charlottesville-Lynchburg road crosses that stream. Here the 

anorthosite is cut by numerous parallel shear zones 

that have been a site for extreme alteration of the 

anorthosite to amphiboles, micas, and clinozoisite. 

Other zones only a few centimeters in width contain 

minerals of a pegmatitic character.

One specimen contains microcline, muscovite, oligoclase, and quartz, named in the order of their abundance. Minor minerals are clinozoisite and apatite 

associated with muscovite in irregular veinlike areas. 

The microcline is nearly fresh, but the plagioclase shows 

the usual alteration products—muscovite and clinozoisite. These plagioclase areas seem to be remnants 

of replaced anorthosite, but the grains are commonly 

surrounded by narrow zones of slightly more sodic 

oligoclase that is almost free from alteration. Seemingly a little fresh material has been added to these 

grains subsequent to their partial replacement and 

alteration. The microcline contains varying proportions of perthitic albite. The quartz sends veinlets 

and rounded lobes into areas of feldspar and is clearly 

later than these minerals but may be of approximately 

the same age as the muscovite. No titanium minerals 

were observed in the pegmatitic lenses.

Other lenses in this locality are composed of an aplitic 

rock. One sample is dominantly microcline with less 

oligoclase and quartz, and another is largely oligoclase. Associated with these lenses are others composed 

of a very fine grained aggregate in which clinozoisite 

is the dominant mineral, but with a little colorless 

garnet, veinlets of quartz and a little pyrite.

The immediate contact is not well exposed along the 

north border of the anorthosite mass, but a road cut at 

the Massies Mill School lies near this contact. Lenses 

of material that is related to the anorthosite intrude 

the schistose country rock. These are small dikes as 

much as 10 centimeters in width. They are composed 

of white feldspar, lenses of blue quartz, and a few grains 

of rutile. The microscope shows a rock composed 

largely of perthitic microcline. The perthite grains 

are about 1 millimeter in diameter and are surrounded 

by a zone of nonperthitic microcline, albite, and quartz. 

The rock is less altered than the anorthosite, but the 

same group of minerals have formed, and clinozoisite 

and sericite. are especially abundant. The rock is 

potassic rather than sodic, as is the anorthosite, and it 

is therefore not a small dike of anorthosite but probably 

an aplitic differentiate of that rock. The abundant 

blue quartz, the similar alteration, and the disseminated 

rutile indicate its close relationship to the anorthosite. 

The quartz forms clear-cut veinlets, which follow the

cleavage planes in the microcline, as illustrated in 

plate 3, D.

FERROMAGNESIAN ROCKS

Several small, sharp-walled dikes have been encountered in the tunnels of the American Rutile Co. 

Some of them are very fine grained, and others are 

moderately coarse, but no abyssal rock types have been 

observed. The fine-grained dikes are commonly only 

a few centimeters across, and at least one is much 

branched. They are now highly altered, ard only an 

approximate determination of their original composition 

is possible. However, they were evidently highly 

ferromagnesian rocks composed dominantly of pyroxene 

with subordinate feldspar. In one specimen the 

pyroxene has been completely altered to a very finegrained aggregate of amphiboles and biotite. Little or 

no feldspar remains, the rest having been replaced by 

amphiboles, biotite, epidote, and quartz. Another 

specimen contains a smaller proportion of a palercolored amphibole, and biotite and a larger proportion 

of low-iron epidote and probably represents a rock 

originally richer in feldspar. All specimens contain 

small amounts of apatite, ilmenite, and sphene.

A large dike is a conspicuous feature of the mine of 

the American Rutile Co. This dike is about 8 feet 

wide, is nearly vertical, -and strikes N. 25 C E. It is 

massive, very fine-grained and dense in texture. It 

appears superficially to be much fresher than the 

ferromagnesian dikes above described but l x as undergone the same type of alteration. A microscopic study 

shows that the original rock minerals (plagioclase and 

augite) have been almost completely replaced by 

clinozoisite, fibrous amphiboles, biotite, and chlorite. 

The dike contains numerous areas of pyrite and a dustlike material that is probably ilmenite. It is cut by 

numerous small pegmatitic veins 1 to 4 centimeters 

wide, which are composed essentially of quartz, orthoclase, and calcite. Smaller amounts of pyrite, pyrrhotite, and chalcopyrite are present. Most of these 

pegmatitic veins contain numerous angular inclusions 

of the enclosing dike rock. A microscopic eramination 

shows that most of the inclusions have nearly the same 

mineral composition as the dike rock, although some of 

the smaller ones have been somewhat recrystallized. 

Between the inclusions and the pegmatitic feldspar 

there is a reaction zone in which radial groups of 

chlorite and clinozoisite crystals have developed. 

Locally apatite is very abundant. Calcite is also 

present and is later than feldspar and quartz and 

probably formed at about the same time as the sulficles 

with which it is associated.

Watson and Taber 12 applied the name "gabbro" to 

rocks characterized by feldspar and lenses of pyroxene—a name which implies a primary pyrogenic origin. 

Some feiTomagnesiaii facies of the anorthosite may have

Watson, T. L., and Taber, Stephen, op. cit., pp. 191-192.
PETROGRAPHY

had such an origin, but the type of material that is well 

represented in the mine of the American Rutile Co. 

seems to have originated in a cliffeient way. These 

ferromagnesian lenses are composed of the pyroxene 

clinohypersthene, described on page 11, and its alteration products. They are believed to consist of a secondary material that has replaced feldspar, and so their 

origin will be discussed in the section on origin rather 

than in this section.

QUARTZ LENSES

Quartz that is commonly blue or gray occurs as 

lenses or veinlike masses, which are locally present 

throughout the anorthosite area. These bodies seem 

to be most abundant in areas of marked alteration of 

the anorthosite and are especially abundant where 

there is a large concentration of ferromagnesian minerals, as in the workings of the American Rutile Co. at 

Roseland. Quartz is abundant on the Bryant farm, 

where it is associated with rutile. Quartz also occurs 

in lesser amount in areas of only minor mineralization 

as rather narrow, sharp-walled veins cutting anorthosite.

NELSONITE

DEFINITION

The Roseland district is the type locality for a rock 

composed essentially of apatite and rutile, or apatite 

and ilmenite, which Watson 13 called nelsonite, after 

Nelson County. The following varieties of nelsonite 

have been listed by Watson and Taber: 14 Ilmenite 

nelsonite, rutile nelsonite, magnetite nelsonite, biotite 

nelsonite, hornblende nelsonite, and gabbro nelsonite.

DISTRIBUTION AND OCCURRENCE

In describing the distribution of the nelsonite bodies 

Watson and Taber 15 say:

The nelsonite dikes usually occur not far from and distributed 

along the border portion of the syenite (anorthosite), with most 

of them confined to the syenite area, but some are found in the 

outside gneiss near the contact. The rutile-bearing variety of 

nelsonite is confined within the limits of the syenite, but the 

ilmenite nelsonites free from rutile, which are more numerous 

within the syenite area, are found in the outside gneiss near the 

contact.

Magnetite nelsonite is found in the surrounding gneiss, but 

does not occur in the syenite.

The size and shape of the bodies are described as 

follows: 16

The size of the dikes varies greatly. Several of the more 

persistent ones may be traced along their strike for considerable 

distances. In length the dikes range up to 2,000 feet, as exposed 

on the surface, but lengths of several hundred feet are more 

common; in width from a few inches up to 65 feet or more.

w Watson, T. L., Mineral Resources of Virginia, J. P. Bell, Lynchburg, Va., 

p. SOO, 1907.

14 Watson, T. L., and Taber, Stephen, GPology of the titanium and apatite deposits 

of Virginia: Virginia Geol. Survey Bull. III-A, p. 104, 191.3.

is Idem, p. 101.

IB Idem, p. 102.

Though dikelike in character, the nelsonite bodies are subject 

at times to considerable irregularity in outline. Several of 

them are lenticular in shape, and where the more continuous 

bodies have been exposed for some distance they are found to 

pinch and swell both in dip and along the strike. In some 

instances the dikes before pinching out split into several parallel 

stringers. They trend in every conceivable direction, but northeast and southwest is the dominant direction of strike.

Usually the boundaries between the dikelike bodies of nelsonite and the enclosing rock are sharply marked, but in places- there 

is a gradation between the two, which is especially true of the 

rutile nelsonites.

ILMENITE NELSONITE

A few of the nelsonite bodies are simple in mineralogy, 

being composed almost wholly of apatite and ilmenite 

or rutile; but other varieties are made up of a number 

of minerals and are extremely variable in mineral composition within short distances.

The type of ilmenite nelsonite known as "hard ore" 

is composed clominantly of ilmenite and apatite, with 

only minor amounts of accessory minerals. The apatite 

is commonly rounded and embayed, as in the rutile 

nelsonite, and appears to be slightly older thg,n ilmeiiite, as rare vemlets of ilmenite fill fractures in it. 

(See pis. 14, A, and 17, D.} A specimen of ilmenite 

nelsonite obtained half a mile west of Rose Union, 

with almost no accessory minerals, contained 73 percent of ilmenite and 27 percent of apatite by weight 

and is illustrated in plate 14, B. The hard ore 

type of nelsonite is commonly the only one resistant 

to weathering and so forms abundant float material. 

Thus it appears from the surface indications to be 

more abundant than other typos, although this is not 

true for most of the deposits. A type of hard ore with 

small amounts of biotite and actinolite forms the large 

ilmenite body controlled by the National Lead Co. on 

the Bob Hite farm, about 1 mile northwest of Roseland, 

and a representative sample has approximately the 

following mineral composition by weight: Ilmenite, 64 

percent; apatite, 27 percent; biotite, 5 percent; actinolite, 4 percent. The biotite fills veinlets and fractures 

in ilmenite and apatite. (See pi. 18, C, D.} Some of 

this biotite forms very fine aggregates, but a few individual grains reach 0.5 millimeter in diameter. Another specimen from the same locality contains r.bout 

20 percent of biotite.

The best exposure of ilmenite nelsonite available for 

detailed study is that of the Southern Mineral Products Corporation on the Piney River near the southeast 

border of the anorthosite mass. Here extensive opencut mining has given a section across one ol the largest 

ilmenite bodies of the region. Operations except for 

prospect shafts are still confined to the zone of weathering, but some of the harder lenses are fairly fresh. It 

has been possible to make thin sections of even the 

most weathered material and determine the minerals 

and their relations. These sliow that weathering has 

resulted less in chemical than in mechanical breakdown of the minerals.
TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

The materials of this ilmenite body are extremely 

variable, and the character of the different lenses may 

change abruptly or may be transitional over many feet. 

A schistose structure is noticeable in much of it (see 

pis. 13, D, and 15, C, D) and seems to indicate development in a rock that had been closely sheared. Some 

of the more abundant types of material are described 

below and indicate the extreme variability in mineral 

composition.

Part of the body is composed largely of ilmenite and 

alteration products of apatite and makes a hard ore 

that forms a resistant float on the surface. Small 

amounts of magnetite fill minute cracks in ilmenite and 

are evidently later than the ilmenite.

Another specimen contains minor proportions of 

ilmenite enclosed in a groundmass made up largely of 

wisplike areas of partly altered biotite, which are 

roughly oriented, giving a schistose structure, as shown 

in plate 15, D. The biotite has been partly altered 

to greenish chlorite. A small amount of actinolite is 

present, and many areas of quartz have been partly 

replaced by biotite and actinolite. A nearly similar 

rock has areas of chlorite 10 to 15 millimeters long that 

extend in the direction of schistosity except where 

molded around apatite or ilmenite grains. Other areas 

are composed largely of actinolite, which is commonly 

associated with small amounts of unreplaced auartz.

A related type of material contains a few areas of 

partly replaced andesine, as shown in plates 14, C, and 

15, but most of the feldspar has been completely replaced by a fine-grained aggregate of biotite, quartz, 

and fibrous actinolite. Some of the biotite areas retain 

a ghostlike structure derived from the lamellar antiperthite of replaced plagioclase. Other areas of fibrous 

actinolite appear to represent completely altered pyroxene grains. A light reddish-brown type of hornblende 

has been partly altered to greenish hornblende, and 

fresh green hornblende that forms euhedral or subheclral crystals is abundant. Biotite is most abundant 

as fine-grained aggregates, but individual grains are 

also present and reach a maximum diameter of 1 millimeter. These have been partly altered to chlorite.

A friable reddish-brown material is composed of 

sparse ilmenite and apatite grains in an earthy groundmass. A microscopic examination shows about 15 

percent of ilmenite and 13 percent of apatite by weight, 

in a groundmass composed of very finely granular 

biotite and its vermiculitelike alteration products. A 

small amount of partly replaced quartz is present, but 

the original feldspar has been completely replaced by 

biotite. Biotite fills numerous small veinlets in the 

apatite and is therefore later.

One lens has a friable, earthy appearance and carries 

only a few percent of apatite and ilmenite. A microscopic study shows that the rock is made up dominantly 

of very fine-grained actinolite with varying proportions

of fine grained interstitial biotite and locally quartz. 

Some areas still retain andesine, which has been only 

partly replaced by secondary minerals, as shown in 

plate 15.

A prospect pit has penetrated unweathered hornblende nelsonite that is dark gray-green. It is strongly 

schistose, with a silky luster on the cleavage surfaces, 

due to the parallel orientation of the hornblende and 

chlorite grains. A microscopic study shows that the 

most abundant mineral is hornblende, wluhh. forms 

parallel groups that are molded around apatite and 

ilmenite grains and augenlike aggregates, as illustrated 

in plate 13, D. A few of these augen retain the albite 

twinning of the original feldspar, as shown in plate 15, C, 

but in most of them the feldspar has been recrystallized 

into fine grained augenlike aggregates of albite, quartz, 

and hornblende that are bounded by the enclosing zones 

of hornblende. Other specimens of the same material 

contain compact masses of fibrous hornblende that is 

an alteration product of augite. A few areas of biotite 

partly altered to chlorite are commonly present. 

Apatite is cut by small veinlets of ilmenite, and both 

apatite and ilmenite by veinlets of hornblende. A 

small percentage of pyrite is associated with ilmenite.

A small lens of anorthosite that occurs in the nelsonite 

body shows the beginnings of the replacement that when 

carried to completion produced the augen structure in 

the nelsonite just described. The rock is composed 

largely of plagioclase showing albite twinning but lacks 

the antiperthitic microcline that characterizes most of 

the anorthosite. The rock eivdently contained a small 

proportion of augite, which is now a hornb^nde aggregate. The plagioclase has been partly replaced by 

hornblende, as shown in plate 4, D. Parallel g warms of 

hornblende needles have formed and show traces of the 

schistosity that is greatly accentuated in the nelsonite. 

In a few areas the plagioclase has recrystallized into an 

aggregate of quartz, albite, and hornblende, as in the 

augen of the nelsonite. Small amounts of ilmenite and 

apatite have been introduced along shear zones. Other 

specimens of highly altered anorthosite found near the 

contact with nelsonite show more nearly complete replacement and are intermediate between the nelsonite 

and anorthosite specimens just described.

A mass of unusually hard, barren rock, now removed, 

occurred within the nelsonite body. A microscopic 

study shows that this rock is andesine anorthosite only 

slightly modified through replacement by nelsoniteforming materials and associated secondary silicates. 

That is, it is essentially the same as the material of the 

disseminated deposits. The composition is approximately quartz, 15 percent; altered pyroxene, 5 percent 

ilmenite, 5 percent; apatite, 2 percent; and the remainder 

andesine in grains that average a little les^ than 1 

millimeter in diameter and have been partly replaced 

by finely disseminated hornblende, clinozomte, and
PETROGRAPHY 9

muscovite. Between this horselike mass of feldspar 

rock and a lean biotite nelsonite is a transition zone 

about 18 inches wide.

Ilmenite-bearing rocks that contain varying proportions of pyroxenes and biotite, or their alteration products, occur in several -places in the region. Some of 

these have been described as gabbro-nelsonites by Watson and Taber, 17 but others are so poor in ilmenite and 

rich in secondary amphiboles that they are best described as amphibolites. These have no commercial 

value and have been little prospected, and fresh material for study is almost lacking. However, shallow pits 

and float material show significant relations.

A partly weathered and friable amphibolite nelsonite 

from the Bryant farm gave fairly satisfactory thin sections that permitted a determination of the minerals 

and their relations. They all contain small augenlike 

remnants of anorthosite enclosed in fine-grained mineral 

aggregates containing pyroxene, amphiboles, biotite, 

garnet, quartz, apatite, and ilmenite, as shown in plate 

13, A, B, C. The relations which indicate that these 

are secondary minerals are described in detail in the 

section on replacement processes (pp. 19 and 20).

A small nelsonite body cuts the gneiss near the Lynchburg-Roanoke road about 4 miles east of Bedford, and 

about 30 miles southwest of the Roseland anorthosite 

area. The mineralized zone is not well exposed but is 

only a few feet wide. It shows a banded structure, and 

a zone near the center, perhaps 50 centimeters wide, 

is composed largely of ilmenite. On each side of this 

are zones that are strongly schistose in structure and 

composed of biotite with lessor amounts of ilmenite. 

This appears to grade into schistose material composed 

of biotite, ilmenite, and quartz. This, in turn, appears 

to grade into gneiss, as there seems to be no sharp contact between nelsonite and country rock. A few rods 

away hard float material occurs whose relations to the 

material just described cannot be determined. This 

rock has the following mineral composition: Green 

hornblende, 50 percent; cummingtonite, 18 percent; 

ilmenite, 13 percent; apatite, 18 percent; and biotite, 

1 percent. Small amounts of quartz and sphene are 

present. The two amphiboles are described in detail 

on pages 12 and 13.

RTJTTLE NELSONITE

A small body of rutile nelsonite was mined for its 

rutile during the summer of 1939 by the American 

Rutile Co., and has permitted the study of a type of 

deposit not previously available. This deposit is about 

a quarter of a mile southwest of Roseland, on the Giles 

property, near the junction of Possum Trot Branch and 

the Tye River.

The rutile nelsonite body is a very irregular lens that 

is about 25 feet in its longest dimension (east-west), 

has a maximum thickness of 8 or 10 feet, and has been

17 Watson, T. L., and Taber, Stephen, op. cit. (Bull. Ill-A), pp. 138-145.

followed to a depth of about 14 feet where it is underlain by anorthosite. The southeast wall is very irregular and gives the ore body its distorted shape.

The ore body is in almost direct contact with altered 

anorthosite on the north side, but on the south intense 

shearing has produced a zone of sericite schist 1 fcot or 

more wide. This zone is made up of sericite, finegrained plagioclase, and a few large residual areas of 

antiperthitic plagioclase. Outside of the zone of intense 

shearing is a wider zone where narrow shear zones alternate with highly altered anorthosite. The only other 

minerals observed in the sericite schist are a very little 

clinozoisite, rutile that has been largely altered to leucoxene and sphene, and a little graphite that is concentrated in thin lenses.

The very close fracturing of the narrow east border 

of the rutile nelsonite is illustrated in plate 19, A, B, 

where the white areas and veinlets represent leucoxene 

(sphene) that has developed in fractures and shear 

zones in rutile (black). In the upper part of the Fr>ecimen shown in figure A replacement has gone so far 

that only small individual areas of rutile remain. The 

nearly horizontal gray zones in figure B and the diagonal zone in figure A represent areas where shearing has 

been so intense that a schistose structure has been produced. The white area on the right in figure A represents a lens of highly altered anorthosite. Figure C represents a small mass of rutile, with irregular tongues, 

and isolated areas of rutile in anorthosite. The gray 

areas are leucoxene (sphene).

A study of thin sections shows inclusions of muscTvite 

in rutile or apatite, and these probably represent recrystallized sericite or anorthosite. Where anortliosite 

is in contact with rutile nelsonite there is an abundance 

of fine-grained sericitic muscovite and a very little 

chlorite.

The alteration product of rutile is in part typical 

leucoxene in appearance, but much of it is cor.rsergrained and permits a determination of the indices of 

refraction, which are those of sphene. Chemical tests 

show the presence of essential amounts of calcium and 

confirm the mineral as sphene. Small veinlets of coarser 

sphene cut the fine-grained material in a few thin sections. The fine-grained typical leucoxene is also spline. 

(See p. 14.)

A body of feldspar 1 foot or more across was encountered within the most massive part of the rutile 

nelsonite. This body is dark gray and contains abundant sericitic muscovite, but it retains the structure and 

mineral character of typical antiperthitic plagioclase. 

The rutile nelsonite in most of the lens is very maesive, 

with grains of rutile and apatite averaging 1 to 2 millimeters in diameter. The richest portion runs 75 to 80 

percent of rutile, but in much of the body, especially 

along the east border, apatite is more abundant. Near 

the east border and including the closely fractured part 

of the lens the rutile is coarser-grained and some grains
10 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

are 1 centimeter in diameter. In this altered part of 

the vein much ilmenite has formed along fractures in 

rutile, as illustrated in plate 19, D. The alteration to 

leucoxene or sphene illustrated in the same figure 

evidently occurred after the introduction of ilmenite. 

In the finer-grained, more massive part of the ore body 

alteration has been slight, and only small amounts of 

ilmenite, sphene, and leucoxene have been formed. 

However, sparse granular ilmenite is disseminated 

throughout the body, a little pyrite forms disseminated 

grains, and later pyrite forms films on fracture planes.

MINERALOGY

The minerals of the Roseland anorthosite and the 

related dikes, veins, and nelsonite bodies are described 

in the following sections. The relations of these minerals to one another and their paragenesis are discussed 

in detail in another section of this report (pp. 15-22). 

The feldspar of the anorthosite composed of andesine 

and its enclosed microcline, a little quartz, and the 

pyroxene of the ferromagnesian facies are believed 

to be primary pyrogenic minerals. Apatite, rutile, 

ilmenite, magnetite, biotite, muscovite, amphiboles, 

clinozoisite, garnet, most of the quartz, chlorite, vermiculite, serpentine, sphene, graphite, pyrite, chalcopyrite, pyrrhotite, and calcite are believed to be 

secondary.

Antiperthitic andesine.—The primary feldspar of the 

andesine anorthosite is the blue-gray antiperthitic 

plagioclase whose occurrence is described on pages 3 and 

4. A microscopic study shows that it is composed of 

andesine, enclosing minute lamellae of microcline, which 

are very regular in distribution, as shown in plate 3, C. 

These lamellae are about 0.003 millimeter thick, 0.03 

millimeter wide, and 0.1 to 0.3 millimeter long, and they 

commonly lie with the greatest length perpendicular to 

the trace of the albite twinning in sections parallel to 

(001) and make an angle of 73° to 75° with the trace of 

the (001) cleavage in sections parallel to (010). This 

orientation corresponds with the plane (701), which is 

the commonly observed direction for both perthitic 

and antiperthitic intergrowths of feldspar. Another 

set of intergrowths cut the first and were evidently 

formed later. These later lenses are about 0.027 millimeter wide or almost 10 times as wide as those of the 

other set. In sections cut parallel to (001) a large 

proportion of these coarser lamellae are roughly perpendicular to the earlier set and parallel to the albite 

twinning (010) as shown in plate 3, C. In some areas 

this second set of lamellae is very irregular in orientation and distribution, and in a few areas they are 

entirely absent. This uneven distribution is in contrast with the very even distribution of the earlier 

fine-grained set.

The even distribution, fine texture, and early formation of the first set of lamellae indicate that they are the 

result of exsolution in the solid state of an originally

SiOAloO

Fe2 03 (total Fe) _ _

MgO-_-__________

Na20_____________

.._ 61.44

.__ 23. 47

— .20

__. .05

___ 5.00

__. 5. 94

___ 3. 92

BaO__ _ ____

H_0-_______

HaO+. ______

________ 0.19

________ .03

________ .20

________ .10

100. 54

homogeneous feldspar, as suggested by Warren. 18 The 

later, coarser-textured, and irregularly distributed 

perthite appears to be the result of partial replacement 

of the feldspar through deuteric reaction, as described 

by Andersen. 19

The following chemical analysis of carefully selected 

primary feldspar from the mine of the American Rutile 

Co. at Roseland has been made in the chemical laboratory of the United States Geological Survey.

Analysis of antiperthitic feldspar of Roseland anorthosite 

[J. G. Fairchild, analyst]

A calculation of the mineral molecules present gives 

the following proportions:

Molecular proportions of antiperthitic feldspar of Roseland 

anorthosite

Orthoclase_____.__ 25.1

Albite___________ 51.0

Anorthite_ ___________ 23.4

Celsian. 0.5

100.0

The small aplitic dikes that cut the country rocks 

hi a road cut at the Massies Mill School are composed 

of perthitic microcline, together with a little rutilated 

quartz and a few grains of rutile. The very fine, evengrained perthite of the exsolution type is illustrated in 

plate 3, C. Surrounding the perthitic microcline are 

small amounts of perthite-free microcline.

This calculation of the molecular proportions indicates that the plagioclase has a composition of Ab68 . 5 , 

a close check on the result based on the indices of refraction, which indicated a composition of /b70 . The 

antiperthitic feldspar is illustrated in plate 3, C.

The granulated feldspar has more variable properties 

than the feldspar from which it is derived. Most of 

it has a composition, as indicated by the indices of 

refraction, only slightly more sodic than the ungranulated material, and nearly all of it contain-" antiperthitic microcline similar to that in the ungranulated 

material. Minor portions range all the way from 

andesine to albite, but the abundance of included 

alteration products makes it difficult to determine 

closely the composition by optical methods.

The augenlike areas of feldspar at the swirrming pool 

on Tye River 1 mile southeast of Massies Mill (see pi. 

10) are composed dominantly of microcline with enclosed perthitic lenses of oligoclase. An unusually large 

proportion of this microcline has been replaced by a very 

coarse myrmekite, an intergrowth of plagicclase and 

quartz. This secondary plagioclase, together with the

is Warren, C. H., A quantitative study of certain perthitic feldspars: Am. Acad. 

Arts and Sci. Proc., vol. 51, No. 3, 1915.

» Andersen, Olaf, The genesis of some types of feldspar from grarite pegmatites: 

Norsk geol. tidsskr., Band X, Heft 1-2,1928.
MINERALOGY 11

primary perthitic oligoclase of the augen, has been 

much, altered to a fine-grained cloudlike material that 

appears to be a mixture of actinolite and clinozoisite, 

whereas the microcline has remained nearly fresh.

Microdine.—In its most widespread occurrence microcline is present as antiperthitic lenses in andesine, as 

described in a preceding section. The augen gneiss 

contains a large proportion of microcline, and very 

small amounts occur as interstitial material between 

andesine grains in the anorthosite. Small pegmatitic 

lenses that locally cut the anorthosite are composed 

largely of microcline. The microcline is much less 

subject to alteration than the andesine and is commonly 

fresh in appearance but has been locally replaced by 

myrmekite.

Rutilated quartz.—A pale grayish-blue quartz is one 

of the most widely distributed minerals in the Roseland 

district, where it occurs as irregular masses associated 

with ferrornagnesian lenses and as veins cutting anorthosite. In the earlier workings of the American Rutile 

Co. masses of such quartz several feet across were 

encountered. In many places in the district the surface 

is mantled by fragments of the blue quartz that no 

doubt were derived from veins. On the Bryant farm 

such quartz is associated with rutile or with apatite, 

similar to that shown in plate 12, B. The blue quartz 

is coarse-grained but nowhere shows euhedral crystal 

form, as it seems to have been formed by the replacement of feldspar and not by the filling of cavities.

Great numbers of minute rutile needles with diameters 

that commonly range from 0.3 to 0.5 micron are enclosed 

in the quartz. The blue color is caused by the selective 

reflection of short blue light waves by these rutile 

crystals, whose diameter is near the optimum for the 

reflection of the shorter light waves. A large proportion of the rutile needles lie parallel to the basal plane 

(0001) of the enclosing quartz and make an angle of 60° 

with one another, as shown in plate 5, A, which is 

reproduced from a photograph of a basal section of 

the quartz. It seems evident, therefore, that the 

distribution and orientation of the rutile are controlled by the trigonal symmetry of the quartz.

Clinohypersihene.—A high-iron member of the pyroxene group is one of the essential minerals of the 

ferromagnesian lenses hi the andesine anorthosite and 

probably also of the oligoclase anorthosite, the nelsonite 

amphibolites, and the dikes. In the lenses it was 

originally coarse-grained, and crystals 15 centimeters or 

more in length are not rare. (See pi. 9.) In the hand 

specimen it is very dark gray, but in thin section or 

small grains it is practically colorless, but occasionally 

shows a famt lavender pleochroism.

The optical properties are as follows: Indices of refraction a =1.6 94, )8=1.710, 7=1.715; birefringence 

0.021; optical character (—); 2V=62°; dispersion 

r^>v; 7=b, Z inclined 44° to c; colorless or with faint

SiOa— ----------- ____________

Ala08 ______-_-___---_-_-_-_-_-

Fe2O3— ---------------------

FeO

MgO-----------------_-------

CaO___--------_----------__

MnO_--_------------_--------

TiOj-------------------------

HaO- — ------__---------_--

H2 0+ — _____________________

Analysis

52 02 

2 40 

55 

21 46 

21 60 

1 90 

16 

44 

06 

34

100. 93

Molecular ra*.lo

0 8661 

02351 

0034J 

29981 

5320 1 

0339 f 

0023J

0. 8661 

.0269

. 8660

lavender pleochroism in thin section. Much of the 

material closely twinned parallel to (100).

Chemical composition cf dinohypersthene 

[J Q. FairchiM, analyst]

This corresponds with the following mineral composition :

Mineral composition of dinohypersthene Molecular percent 

Clinoenstatite (MgO.Si02 ) ________________ 42. 0

Clinoferrosilite 20 (FeO.SiO2) _______________ 40. 5

Diopside (MgO.Ca0.2SiO2) ___________ ^ __. 7. 5

20 Bowen, N. L. "Ferrosilite" as a natural mineral; Am. Jour. Sci., 5th sei., vol. 

30, pp. 481-494, 1935.

In the ferromagnesian lenses, this pyroxene is pr.rtly 

altered to amphiboles. In many specimens only residual areas remain in a groundmass of fibrous actinolite 

and in the nelsonite amphibolites and ferromagnesian 

dikes the alteration is almost complete.

Clinozoisite.—The low-iron member of the epidote 

group, clinozoisite, is one of the most widespread 

minerals of the Roseland area. It occurs most widely 

as microscopic grains disseminated in feldspar, wheve it 

forms irregular aggregates, tuftlike areas, or rarely 

elongated prisms that reach a maximum length of 0.2 

or 0.3 millimeters. (See pi. 4, A.} More rarely it 

forms colorless veins not over 1 centimeter wide (see 

pi. 3, ^1), which resemble quartz hi the hand specimen, 

and so the mineral is easily recognized only under the 

microscope. A few small vugs in highly altered feldspar are lined with euhedral crystals that are rarely 

more than 2 millimeters in length. The high index of 

refraction and aggregate character cause the disssmiiiated clinozoisite to disperse light and appear gray in 

thin section. The clinozoisite in small veins occurs as 

anhedral grains 0.1 to 0.4 millimeter in diameter, which 

show a brilliant indigo-blue color under crossed nicols.

The indices of refraction are «= 1.700, /3= 1.703, 

7=1.706, and 2V is near 90°. Optical character (+). 

Colorless and water-clear in small grains. Locally a 

higher-iron member of the clinozoisite-epidote group of 

minerals is present. A dull greenish-gray specimen 

from the mine of the American Rutile Co. has indices 

of refraction a— 1.722, 7=1.746, which correspond to 

a low-iron epidote.
12 TITANIUM DEPOSITS OF NELSON AND AMHEEST COUNTIES, VIRGINIA

The following analysis represents selected material 

from one of the veinlets about 1 centimeter wide:

Chemical analysis of clinozoisite 

[J. G". Fairchild, analyst]

SiO,— --------- ____________

Al_O__-_-----.___-_-_____--_

Fe_OB— --------------------

FeO

MgO_----_-_____-_-________

CaO_____----______-______-_

K2O__-______^_______. ______

Na_O— .__-__--__---_- ______

H2 0 + _. _-___-__-_________-_

H_O--___--_-_.___-________

TiO2

F

Less O = F_.____ ________ .__._

Analysis

39. 96 666

30. 59 299

3. 23 20

. 60 8

. 05 1

23. 58 420

I 13 ) - 16

2.00 111

None

.05

.02

100. 21 

. 01

100. 20

Molecular ratio

666 or 6X111.

J319 3X106.

429 4X107.

Ill 1X111.

This analysis corresponds very closely with the 

chemical formula H2O.4CaO.3Al2O3.6SiO2, with only 

3.23 percent of Fe2O3 proxying A12O3 . Fluorine has not 

been generally recognized in the epidote group of 

minerals; in fact, it has not been the custom to look for 

it, but its presence is not surprising.

Amphiboles.—Various members of the amphibole 

group are among the most abundant and widespread 

minerals in the Roseland area. Actinolite or hornblende is an alteration product of pyroxenes in the 

oligoclase anorthosite and in ferromagnesian lenses and 

dikes. Along the borders of channels of active mineralization in the anorthosite, in ferromagnesian dikes, 

and in anorthosite reminants in nelsonites actinolite 

has replaced feldspar. In parts of the anorthosite 

farther from channels of active circulation, tremolite 

or hornblende has formed within feldspar grains, as 

shown in plate 4, D.

The hornblende of t 

veinlike masses which ' 

as shown in plate 9, 8 

areas of it.

The indices of refraction as given by Watson and 

Taber are c_= 1.620, 7=1.649. The indices of refraction as determined by the writer on a specimen of 

similar material from the mine of the American Rutile 

Co. are a= 1.618, 7=1.642. These figures indicate 

that this specimen was very slightly lower in iron than 

the one studied by Watson and Taber.

The tremolite occurs as minute grains disseminated 

in feldspar, from which it cannot be separated for 

accurate study, but the index of refraction is evidently 

low, indicating a low iron content.

Much of the amphibole secondary to augite in the 

small intrusive dikes is distinctly green and slightly 

pleochroic and is evidently hornblende.

One of the most abundant occurrences of amphiboles 

is found in the nelsonite body of the Southern Mineral 

Products Corporation, where sheared anorthosite has 

been replaced by hornblende, as shown in p] ates 13, D, 

and 15, C. The most intense replacement has occurred 

along shear zones, but disseminated hornblende has also 

formed within the augenlike residual areas of anorthosite. There has been a similar replacement of sheared 

anorthosite in the amphibolite nelsonite from the 

Bryant farm, as illustrated in plate 13, A, B, C.

Two amphiboles form abundant minerals in a small 

ilmenite-bearing lens in replaced schist about 4 

miles east of Bedford, Va., described on page 9. A 

microscopic study revealed a deep-green hornblende 

and a colorless cummingtonite. These two types 

formed distinct individuals with sharp boundaries and 

no zonal relations. A few crystals are composed of 

green amphibole at one end and colorless cummingtonite at the other, but the change is invariably abrupt. 

These relations indicated that there was no molecular 

isomorphism between the two types and it seemed advisable to separate the two and have them analyzed. 

The results are given in the following table.

Analysis of amphiboles

SiO2 ______ __________ 51.31

A12O3 -__-_--_______- None

Fe_O3 -_-____________ 5.31

FeO________________ 10.12

MgO_______________ 17.93

CaO________________ 10.95

__-__________ .22

_____________ .29

erromagnesian lenses forms 

3 replaced clinohypersthene 

commonly enclose residual

md indices of refraction of 

iven by Watson and Taber. 21

e from Nelson County 

ton, Jr., analyst] 

H2O-______________ 0.04

H2O+_____ _________ 1.26

TiO2 ________________ 3.00 

MnO___ _ .11

P2 O5 ______ __________ None

CO2 _ _______________ Trace

100. 54

p. cit. (Bull. III-A), pp. 219, 220.

SiOs------ — — - — --------

Al_Os- — ---- — — — — -----

Fe_O,___-_ — — -_ — — — __

FeO___— -------_----_-

MgO—— ---_--- — ---

CaO_--__ --- — __- — — -- —

Na2O-_. _________________

K_O____------_------_-

H.O__. _---_--.___-_-_-_-

H_0+_-_--__ — --- — -

TiO2

MnOt— ------------------

Total--.. — ------ _

i

51.50 

1. 76 

. 12 

33.42 

10.38 

None

} . 30

1. 65 

. 24 

. 53

99. 90

2

50. 74 

.89

33. 14 

10.31 

Trace 

f . 54 

I Trace

} * 3. 04 

1. 77

100. 43

3

46.20 

6. 94 

4. 50 

21.00 

7.48 

10.02 

.84 

.48

{ 2.66 

.33

. 24

100. 03

i Ignition loss.

Analyses 1 and 3 by J. G. Fairchild; analysis 2by Smith and Brush. Smith, J. L., 

and Brush, G. J., Reexamination of American minerals: Am. Jour. Sci., 2d ser., vol. 

16, p. 48, 1853.

Analysis 1 shows a typical cummingtonite and is surprisingly similar to an analysis of the type ma terial from
MINERALOGY 13

Cummington, Mass., given in column 2. The analysis 

of the green hornblende given in column 3 shows that 

it is a high-iron hornblende. The most fundamental 

chemical difference between the two associated but 

nonisomorphous amphiboles is the presence of CaO in 

the hornblende and its absence in the cummingtonite, 

but there is also a higher content of Fe2O3 and A12O3 

in the hornblende.

The optical properties are as follows:

Birefringence- _________

Extinction. __ ___

Optical character.

2V-----------------_.

Pleochroism J —

Green hornblende

r«=i. 661———..—

]0=1. 679— ——— ——

[T = l. 687— __ __ ————

0.026_-_________-____

21° _________________

(-)____ ———— ————

65°±50 __-__.________

r

^*> v Qi"iwn cr

(a -25" YG-Y'b citron 

green. 

</3 = 29' GG-Y'i light

Brice green. 

1,7 = 37' GB-i zinc green_

Cummingtonite

a= 1.658.

0 = 1.670.

T = 1.688.

0. 030. 23°.

(H-). - 80° ±5°.

Woo IT

)

None

1 Ridgway color standard.

Micas.—The most widespread mica is a fine-grained 

sericitic muscovite disseminated in feldspar. A small 

amount of moderately coarse grained muscovite is 

associated with biotite in some of the nelsonite bodies, 

and a little is present in small pegmatitelike masses that 

locally cut the anorthosite. A pale-brown biotite of 

sericitic habit has formed around the borders of ferromagnesian minerals or ilmenite, but at a distance of 

not more than a few millimeters a colorless mica has 

formed, and this is found in varying proportions 

throughout the anorthosite. Biotite is associated with 

ilmenite or rutile in several types of nelsonite. The 

index of refraction is high as a =1.665, which, together 

with the light color (reddish brown to pale brown), 

suggests a high titanium but low iron content. The 

biotite of the nelsonite is later than both ilmenite and 

apatite, as it fills fractures in both these minerals and 

locally'has replaced apatite. (See pi. 18, C, D.)

The brown micas commonly show alteration, and 

part of them have been changed to chlorite and part to 

vermiculitelike material. In the upper portion of some 

of the nelsonite bodies the brown mica has weathered 

to a claylike material.

Rutile.—The rutile of the Koseland district shows 

several distinct types of occurrence. The most widespread type forms disseminated grains in the granulated andesine anorthosite. The rutile grains are 

commonly roughly rounded or irregular in outline but 

others are angular, rarely show crystal faces, and the 

diameter commonly ranges from a fraction of 1 millimeter to 10 millimeters. The coarsest type of rutile 

observed is that left on the surface on the Bryant farm, 

three-quarters of a mile south of Claypool, where 

masses as much as 10 centimeters in diameter are

286089—11——2

made up of individual grains 1.5 centimeters or less 

across.

The color ranges from a metallic steely black for some 

of the rutile close to ferromagnesian lenses to mahogany 

red for that disseminated through the feldspar. In 

thin section the rutile commonly ranges from lemon 

yellow to deep brownish orange and shows noticeable 

pleochroism. A few grains are grayish lavender. 

Twinning is usually present.

Watson and Taber give chemical analyses of two 

samples of rutile containing 95.71 and 98.80 percent of 

TiO2 , 0.15 and 0.20 percent of V2O3 , and 0.02 and 0.07 

percent of Cr2O3 .

Analyses of two types of rutile are given below.

Analyses of rutile from American Rutile Co. 

[J. G. Fairchild, analyst]

FeO— ------- --------------------- -

SnO,_ — — --- — — —— ——— —

CaO _— — — — — — _ — — — - — — — — -

MgO___ -______-_- ------------------

Cr2O3— — — — — — —— —— — —— — ——

V,0,._ —— ——— —— ——— — —————

ZrO2, ThOj—— __ --------------------

(Cb,Ta)jO8— --__ —— - — — - — --

TiO2 (by difference)-----.-.----------

H-i-v£k/»i-fi/» 0"i*p. v°ii" v

Brown

iQ. 40

None

None

None

. 04

.28

None

2 None

99.28

100. 00

4. 304

Bla?k

»0. 62

None

None

None

.06

.28

None

2 None

99.04

100. 00

4.280

' Iron calculated as FeO.

8 Less than 0.05 percent, if any.

The foregoing analyses fail to show the cause of the 

variation in color of the two types of rutile, as a rr.nge 

in FeO from 0.40 to 0.62 percent seems insufficient to 

produce the difference, and other elements are alnost 

the same in the two samples. It is probable, however, 

that the dark metallic color is due to the presence of iron 

in two states of oxidation. The darker type is completely free from microscopic inclusions, and small 

grains are as transparent as in the paler type.

The rutile in the rutile nelsonite forms rounded, 

angular, or irregular grains and is similar in appearance 

to those disseminated in the anorthosite, which rr,nge 

from about 2 to 10 millimeters in diameter. It is 

dark brown and is slightly darker than the reddishbrown type of disseminated rutile, but it rarely shows 

the metallic luster of that occurring close to the feeding 

channels.

The crystals of rutile enclosed in quartz (see p. 11) 

are so minute that it is not possible to determine any of 

the optical properties. Measurements of these crystals 

show diameters ranging from 0.3 to 0.5 micron and 

lengths as much as 1 millimeter or more. Thus som e of 

these have a length at least 3,000 times their diameter.

The replacement of rutiile by ilmenitte is described on 

page 18 and pictured in plate 18, C. A few specimens 

show a narrow alteration rim of sphene ("leucoxene,"
14 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

see below), although rutile has in general been much 

less subjected to alteration of this type than ilmenite.

Ilmenite.—The ilmenite occurs in the various types of 

nelsonite, where it is associated with apatite, biotite, or 

altered pyroxenes; disseminated in the anorthosite; and 

in the gneissic border facies. The grains of ilmenite in 

nelsonite and anorthosite reach 5 or more millimeters in 

diameter and are irregular or roughly rounded but 

nowhere euhedral in outline. In the dikes and veins 

with abundant ferromagnesian silicate minerals, the 

minute grains of ilmenite form very irregular, wavy, 

shredlike lenses as illustrated in plate 13, A. Some 

grains of i^hnenite atfe slightly fractured and the cracks 

filled with later biotite and magnetite, but none are 

crushed to the same extent as the granulated plagioclase. 

Where associated with magnetite the ilmenite has a 

brilliant luster and a distinctly purplish color by reflected light, whereas the magnetite has a duller metallic 

gray color. Ilmenite occurs in cleavage planes of some 

of the clinohypersthene (see pi. 14, D), where it forms 

films so thin that they transmit light and show a distinct 

lavender color. Thus the color shown by transmitted 

light agrees with that by reflected light. The replacement of rutile by ilmenite is described on page 18, 

and much of the rutile shows a narrow alteration rim of 

sphene.

Sphene (leucoxene).—Throughout the Roseland area, 

sphene occurs hi the form of typical flattened rhombic 

crystals, and it is especially abundant in the quartz 

monzonite near its contact with the anorthosite.

The sheared east border of the rutile nelsonite body 

on the Giles property (illustrated hi plate 19) has been 

very completely a tered to secondary titanium minerals. Some oi th s material, even though very fine 

grained, may be recognized as sphene by optical 

methods. Other parts are extremely fine grained and 

resemble the material called leucoxene.

The presence of sphene is confirmed by the following 

chemical analysis of a sample made up of the material 

in question, together with smaller amounts of rutile 

and ilmenite and a very little apatite.

Analysis of secondary titanium minerals from the Giles property 

[R. E. Stevens, analyst]

.. . .. -._-._ 13. 6

.__. . ______ 12.4

. _ _ . _ _ _ _ 14. 6

____________ 52.6

R2 O3 . 

CaO_.

PiOB __-____-___-.__-__ 2.0 

F2O_-_-_-_._-. _______ 2.9

98. 1

The approximate absence of other silicate minerals 

indicates that sphene is the source of most of the SiO2 , 

and also of the CaO.

Much of the ilmenite and rutile of the Roseland 

district is enclosed in thin shell-like films of a secondary 

alteration product. This is submicroscopically crystalline and has a very high index of refraction, close to 

that of sphene. An X-ray examination of shell-like 

films of the material enclosing rutile, shows that the

diffraction pattern is that of sphene. The very fine 

grained material associated with the fine-grained sphene 

on the Giles property is no doubt the same.

Tyler and Marsden 21a have studied leuooxene by 

X-ray and found that in most occurrences it was rutile, 

but in one they found it to be anatase. The "leucoxene" associated with the Magnet Cove rutile is 

anatase. (See p. 24.) The Roseland "leucoxene" is 

the first, so far as known, that has been identified as 

sphene.

Magnetite.—Magnetite is associated with ilmenite, 

amphiboles, and biotite in one of the rarer types of 

nelsonite, where it forms grains of about the same size 

and shape as the ilmenite. It is dull metallic gray 

and is much less fresh hi appearance than the ilmenite. 

It also forms small veinlets hi minute fractures in 

ilmenite.

Apatite.—One of the most abundant minerals hi the 

Roseland district is apatite, a charactertistic mineral 

of nelsonite, of which it makes up from 10 to perhaps 

35 percent, as illustrated in plates 14 and 15. It also 

occurs in lesser amounts in the ferromagnesian dikes 

and lenses and close to them in the anorthosite and hi 

the border facies. In the nelsonite it forms roughly 

rounded but not euhedral grains that reach r, maximum 

diameter of 2 to 3 miUimeters. The grains are colorless and nearly transparent to opaque white where the 

mineral is fresh. Apatite also occurs in irregular 

masses in blue quartz on the Bryant farm. (See pi. 

12, B.)

Watson and Taber 22 give the following analysis of 

an almost pure fluorapatite from the mine of the 

General Electric Co.:

Analysis of apatite 

[Wm. M. Thornton, Jr., analyst]

CaO._..._.._- — _.. 54.37 

MgO__- ._____--____ .53

P,08 ---- —— --—'-- 41.30

F____.--.----_-...-. 2.50

Cl—---- — -- — -— .10

SiO2 ---.------------- .33

TiO5 -_.-------------- .20

Fe2O3

O=F-..

. 0. 61 

. . 19

100. 13

. 1. 07

99.06

The indices of refraction are e=1.630, co=1.634.

Minor minerals.—A minor mineral of tl 3 rocks of 

the Roseland district is graphite. It is probably most 

abundant at the old mine of the General E1 metric Co., 

where it occurs in ferromagnesian lerses called 

"gabbro" 23 and to a lesser extent in the anorthosite as 

flakelike grains disseminated in highly altered feldspar.

On the old dumps of the mine are numerous masses of 

a highly altered porous rock composed of andesine, 

quartz, pyrite, clinozoisite, and sericite together with 

several percent of graphite that occurs in flakes 1 or

2i» Tyler, S. A., and Marsden, R. W., The nature of leucoxene: Jour. Sed. Petrology, 

vol. 8, pn. 55-58. 1938.

22 Watson, T. L., and Taber, Stephen, op. cit. (Bull. III-A), p. 223.

23 Idem, p. 229.
ORIGIN OF THE ROCKS AND MINERALS 15

rarely 2 millimeters in diameter. Grains of granular 

quartz are commonly surrounded by films of graphite, 

and the embayment of clinozoisite and the formation of 

films of graphite in cleavage planes in muscovite indicate 

that graphite is later than both these minerals. 

Graphite and pyrite are commonly associated and 

appear to have formed at about the same time.

Small plates of graphite as much as 2 millimeters 

across, occurring sparsely in blue quartz, are present in 

the mine of the American Rutile Co., and very small 

amounts occur in sericite schist bordering the rutile 

iielsonite on the Giles property.

Pyrite, althouth not an abundant mineral, is present 

in varying amounts in nearly all types of rock in the 

region. It is associated with graphite in the old mine 

of the General Electric Co., as described above. It 

occurs as a minor mineral associated with pyrrhotite 

and rarely with chalcopyrite in the ferromagnesian lenses 

(see pi. 9, B), where pyroxenes have been altered to 

hornblende. A very fine grained dendritic type of 

pyrite or marcasite forms gray aggregates (see pi. 4, B) 

in some of the altered anorthosite in the feldspar prospect on the Piney River 1 mile west of the main road 

between Chaiiottesville and Lynchburg. Pyrite is also 

present in many of the nelsonite bodies as small rounded 

grains that average about 1 millimeter in diameter, and 

a specimen of nelsonite from the dump of the General 

Electric Co.'s mine carried about 1 percent of pyrite.

Pyrrhotite is somewhat less abundant than pyrite 

but is widespread and especially abundant in some of 

the lenses of amphiboles that have replaced clinohypersthene. A specimen with about equal proportions 

of amphiboles and partly replaced clinohypersthene 

contains several percent of pyrrhotite in irregular areas 

that reach a maximum diameter of 15 millimeters. 

Associated with this are small amounts of pyrite and 

chalcopyrite.

Where ihnenite and sulfides occur together there 

appears to have been no replacement of one by the 

other, and so the mutual spatial relations do not show 

the relative age.

Sphalerite occurs in a small vein on Alien Creek half 

a mile southeast of Rose Union, where it is associated 

with quartz, pyrite, and a very little galena. This 

vein may be related to the sulfides previously described, 

but the scant specimens available from the old dump 

give no evidence about the mineralization processes or 

the relation to the anorthosite and associated rocks.

Calcite is nowhere abundant but is widely distributed 

ID the anorthosite and associated rocks. It forms rare 

scattered grains in the anorthosite and numerous small 

veins or lenses in the border facies. Near Rose Mills, 

small veins and nests of calcite are especially abundant, 

and irregular masses form an essential part of the 

anorthosite lenses, which cut the country rock near 

the point where the Charlottesville-Lynchburg road

crosses the Tye River. Disseminated grains of calcite 

are commonly present in altered gneissic quartz monzonite near the contact with the anorthosite.

A sooty black cobalt-bearing clay forms small seams 

filling joint cracks in the nelsonite body being mined 

by the Southern Mineral Products Corporation. A 

chemical analysis of this material by R. C. Well^ is 

given below.

Analysis of cobalt-bearing day from Southern Mineral Products 

Corporation's mine

[R. C. Wells, analyst]

SiO2 ____. ___________ 29.41

A12O3 - _--__-_-_-.._- 28. 97

Fe2 O3 -_ __.._.-_.___ 12.20

_-_---_-----_ .18

___-. -------- .60

.--_-. __-.._. .18

__-_____-.--- .26

H,O- 4.65

13.13

TiOj.—— — - — _ — __ 0.76

COj__...___.__.__ None

NiO...__-—.----_. .03

CoO___._. — __--_. 1.51

MnO + O—__-___.__ 8.28

Li2O_ _______________ None

CuO______.___ None

100. 16

This analysis shows that the material is essentially 

a kaolinitic clay with admixed oxides of iron, marganese, and cobalt. The source of the manganese and 

cobalt is not evident, as manganese- and cobalt-bearing 

minerals have not been recognized in the anorthosite 

and associated minerals.

ORIGIN OF THE ROCKS AND MINERALS

The preceding sections of this paper describe the 

general geology and the rocks and minerals of the Roseland district and provide a basis for a consideratior of 

their paragenesis. This involves a correlation of the 

field geology with petrology, mineralogy, chemistry, 

and physics. It includes the origin of the anorthosite 

by differentiation, its mode of emplacement, and its 

physical condition during and after emplacement. It 

considers the relations between the anorthosite, the 

intrusive dikes, the nelsonite bodies, and the secondary 

minerals. It involves the physical and chemical 

character of the solutions that invaded these rocks and 

deposited secondary minerals and endeavors to explain 

the factors controlling mineral formation. This le^.ds 

to a consideration of the method by which these solutions were segregated from their parent rock and the 

manner in which they were transferred to the zone of 

mineral deposition.

The origin of the rocks is not taken up hi the purely 

descriptive section on petrography; the secondary minerals are described there, but then* significance is not 

discussed in detail. The character and mutual relations 

of minerals, more especially the secondary minerals, 

present evidence about the more theoretical problems 

of paragenesis. For that reason description and interpretation are ultimately interwoven in the sections on 

origin. First the rocks of pyrogenic origin are considered.
16 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

These rocks were invaded and more or less modified by 

groups of secondary minerals, whose origin is discussed 

under " Physicochemical processes."

ANDESINE ANORTHOSITE

The character of the Roseland anorthosite, its feldspathic composition with andesine enclosing antiperthitic microcline, and its crushing and granulation 

throughout the area are described in preceding sections. 

This essentially monomineralic character suggests that 

the genetic history of this rock may be similar to that 

of the anorthosites of the Adirondack region.

Anorthosites have been intensively investigated within the last few years, and several geologists have published papers on their mode of origin and emplacement. 

Bowen 24 has advocated a formation by crystal accumulation followed by intrusion of the mushlike crystal 

mass, after which the interstitial liquid material was 

largely squeezed out by filter-press action. He says: 25 

"But of no such rock can it be said that a protoclastic 

structure is an almost universal character, as it can of 

an anorthosite. The structure is evidence of the fact 

that when an anorthosite mass moves it does so only 

with accompanying granulation." Bowen 26 also stresses 

the improbability of a differentiation process that would 

produce magmas having a purely feldspathic composition.

Balk, 27 after a field study of the Adirondack anorthosites, concludes:

A large mass of poorly differentiated parental magma with 

appreciable quantities of suspended solid crystals of labradorite 

and fewer ferromagnesian minerals has advanced in a general 

southwesterly direction, obliquely upward.

During the very long history of intrusion this parental magma 

has differentiated into three rocks—gabbro, anorthosite, and 

syenite. Gabbro and anorthosite are regarded as crystal 

differentiates, produced by the mechanical accumulation of 

solid mineral grains. Syenite plays the role of the mother 

liquor from which the other rocks differentiated. * * *

Driven forward by the constant magma current from northeast to southwest, the individual labradorite clusters have been 

compacted in the southwestern, distant corner of the magma 

chamber. The crystals have rubbed and sheared against each 

other under enormous compression, until the available interstices were tightly cemented by powder of crushed labradorite 

fragments. In proportion as the compression increased, the 

mother liquor has been ejected.

Buddington,28 after a restudy of the anorthosites of 

the Adirondack area, makes the following statements:

All the phenomena are consistent in indicating formation of 

the anorthosite through differentiation from a gabbroic anorthosite magma with a distinct content of volatiles. The hypothesis

M Bowen, N. L., The problem of the aaorthosites: Jour. Geology, vol. 25, pp. 209- 

243,1917; The evolution of igneous rocks, pp. 170-174, 1928.

2* Bowen, N. L., op. cit. (1928), p. 172.

»Idem, p. 170.

" Balk, Robprt, Structural study of the Adirondack anorthosite: Min. pet. Mitt., 

Band 41, Heft 3-6, pp. 411-412, 1931.

28 Buddington, A. F., Origin of anorthosite in the Adirondacks and in general: 

Am. Geophys. Union Trans. 17th Ann. Meeting, Washington, pt. 1, pp. 255, 256, 

1936.

of a rest-magma of the composition of the quartz syenite on 

the one hand, squeezed out from an anorthositic fraction on the 

other, does not satisfy the requirements of the data. * * *

Analogy with stratiform sheets suggests the possibility that 

the anorthosite horizon consisting of bytownite and perhaps 

calcic labradorite may well be present above the p^ridotite shell 

in the interior of the earth. Partial melting of such an anorthosite shell or stratum would yield a gabbroic anorthosite magma 

of the requisite character for the Adirondack typ? of intrusion 

and would be consistent with the generally restricted composition of the plagioclase shown by such bodies. The restriction of anorthosite of this origin to the pre-Car^brian would 

find a natural explanation in higher temperatures locally or as 

a whole, at higher levels in the earth's crust at thi?> period.

The mode of formation of rocks made up of one or 

almost exclusively one mineral has always presented 

an interesting problem in geology and is one of the 

reasons for an especial interest in anorthosites. Investigations of this problem have centered around the 

anorthosites of the Adirondack region. Here parts of 

the anorthosite bodies are composed essentially of 

plagioclase, but they commonly contain small proportions of dark minerals and grade over into almost 

typical gabbros. The plagioclase ranges from labradorite to andesine, with andesine the typical mineral 

in much of the rock.29 Thus the Roseland anorthosite 

is no more sodic than many of the anorthosites of the 

Adirondack region, but on the other hand it is more 

completely free from dark minerals than almost any 

part of those rocks.

Anorthosites are commonly believed to be the result of differentiation from a magma of more normal 

composition. Some process has brought e.bout a segregation of plagioclase, or of a magma that crystallized 

into plagioclase and a little microcline from an earlier 

magma, that perhaps originally had a gabbroic composition. The theory of crystal settling and intrusion 

of a mush of feldspar crystals has been outlined and 

seems to accord with the relationships presented in 

the Roseland district. However, the work of Buddington casts doubt on this explanation for the Adirondack 

region, and so to extend it with certainty to the Roseland district is premature.

The exposures in the Roseland district are so sparse 

that it is not possible to map the significant rock 

structure, as Balk has done in the Adirondacks, and 

arrive at definite conclusions about the direction of 

movement of the intruding mass. No rock corresponding to the syenite that Balk believes to have been an 

interstitial magma squeezed out from the anorthosite 

is present in the Roseland district. Tl °> injection 

gneisses along the border and small pegnaatitic and 

aplitic zones in the anorthosite may perhaps correspond to such material, but these local occurrences are 

not representative of large-scale expulsion of residual 

magma. If such material escaped from the anorthosite, 

most of it must have been deposited at higher levels, 

now largely removed by erosion.

» Idem, pp. 255, 256.
ORIGIN OF THE ROCKS AND MINERALS 17

OLIGOCLASE ANORTHOSITE

The gray granular anorthosite has undergone alteration of the same type as the nearly white andesine 

anorthosite. It is now composed of antiperthitic 

oligoclase of about the composition Ab80, pyroxene 

partly altered to fibrous amphibole, ilmenite, rutilated 

quartz grains that are commonly distributed in zones, 

and disseminated micas, amphiboles, and clinozoisite.

No large residual feldspar masses are present, as in 

the andesine anorthosite, but the marked distortion of 

crystals and the identity of the antiperthitic structure, 

with that in the granulated andesine anorthosite indicate that it has undergone similar granulation, although 

it was probably originally a medium-grained rock. 

The quartz, pyroxene, and ilmenite are in part disseminated through the rock, but large proportions of 

them occur together in lenses and zones that extend 

for several centimeters and produce a schistose structure. 

The quartz shows strain shadows but is ungranulatecl, 

and ilmenite shows only minor cataclastic effects. 

This suggests that the secondary minerals in the lenslike areas have not undergone granulation by dynamic 

forces but were introduced into shear zones by solutions after granulation of the oligoclase anorthosite, 

just as they were in the andesine anorthosite.

In general the same types of disseminated minerals 

are present in the oligoclase anorthosite as in the 

andesine facies. However, ilmenite is the characteristic titanium mineral rather than rutile. The dominant secondary silicate of the oligoclase anorthosite 

is pale-green actinolite, which has formed abundantly 

throughout the feldspar and also as an alteration 

product of augite. In some areas pyroxene has been 

completely altered, but in others residual masses are 

present. Biotite has formed rather than sericitic 

muscovite, as in the andesine anorthosite. Part of 

the quartz may be primary, but much of it occurs in 

small lenses associated with apatite, ilmenite, and 

actinolite-rich areas, where it appears to be secondary.

The oligoclase anorthosite has about the same mega- 

.scopic texture as the gneissic quartz monzonite, and 

the physical relations suggest that it may be a block, 

or a roof pendant of the quartz monzonite enclosed in 

the andesine anorthosite and partly replaced by it, but 

microscopic studies indicate that it is a facies of the anorthosite. If it is altered quartz monzonite, the replacement has been so complete that all primary biotite and 

individual grams of potassium feldspar hare been 

destroyed, and only minerals and mineral relations 

characteristic of the anorthosite are now present.

Near the point where the Roseland road leaves the 

Charlottesville-Lynchburg road and about half a mile 

southeast of the anorthosite body is a quarry where 

the effects of contact metamorphism of the quartz 

monzonite may be observed. Here the plagioclase has 

been highly altered to clinozoisite and sericite, and

much titanium in the form of sphene has been introduced, but the microcline, as in the anorthosite itself, 

has been little altered. Microcline appears to be the 

mineral most resistant to alteration in both the quartz 

monzonite and the anorthosite, and therefore microcline should be expected to persist, to some extent at 

least, in any masses of gneissic quartz monzonite ttat 

had become enclosed in and altered by anorthosite. 

On the other hand, the gray granular rock (oligoclase 

anorthosite) encountered in the tunnels shows no 

individual crystals of microcline, but only the antiperthite that is characteristic of the anorthosite. It 

therefore seems probable that the gray granular rock 

represents simply a facies of the andesine anorthosite. 

Masses of one facies of an anorthosite mass enclosed 

in another seem to characterize many anorthosites. 

(See pp. 23-26.)

QUARTZ LENSES

Some quartz forms definite veins at a distance frcm 

centers of intensive mineralization, but most of it occurs 

in or near such areas, and much of it appears to have 

been introduced into the feldspar together with the 

clinohypersthene lenses. Similar quartz is also abundant as disseminated lenses in the gray granular facies 

of the anorthosite described above, and in the injection gneiss that forms a border facies at Rose Mill. 

(See pi. 16, 5.)

Although quartz is in general more subject to dynamic granulation than feldspars, the large masses of 

blue quartz show almost no granulation, though strains 

are commonly present. This indicates that the blue 

rutilated quartz belongs to a stage of mineralization 

later than the granulation of the anorthosite. This is 

more conclusively shown by the veins of quartz cutting 

the anorthosite and by the veinlets of quartz cutting 

feldspar crystals that may be observed in most of the 

thin sections examined. The blue quartz contains 

abundant rutile needles, and so it is evident that some 

titanium was being introduced at the same time that 

this type of quartz was introduced, although it is not 

clear that this time corresponds with the period of the 

greatest introduction of rutile and ilmenite.

BORDER FACIES

The border facies as developed at Rose Mills is a typical injection gneiss. The lenses of anorthosite material 

have been introduced along the schist planes of the 

invaded rock. This rock was for the most part a bio tit erich quartz schist, but some lenses of altered quartz 

monzonite seem to be present. The sequence of events 

at the Rose Mills locality seems to have been as follows: 

The deposition of a quartz-rich sedimentary materiel; 

its metamorphism, with the development of marked 

schistosity; the intrusion of lenses of quartz monzonite; the introduction of lenses of anorthosite material along schist planes; the introduction of lenses of
18 TITANIUM DEPOSITS OF NELSON AND AMHEKST COUNTIES, VIKGINIA

pyroxenes along shear planes (see pi. 16, B); and the 

introduction of secondary minerals including blue 

quartz, apatite, rutile, ilmenite, amphiboles, biotite, 

and clinozoisite. The physical character of the anorthosite material during its introduction is not clear, 

but it was probably a water-rich magma, perhaps of 

pegmatitic or aplitic character. This is indicated by 

the impregnation by feldspathic material of the schist 

associated with the anorthosite lenses. Subsequent 

mineralization was similar to that in the process 

affecting the entire anorthosite mass.

FERROMAGNESIAN DIKES

Numerous dikes occur in the Roseland district and 

are well represented hi the mine of the American Rutile 

Co. at Roseland and near Rose Mills. These dikes 

cannot all be definitely assigned to a single period of 

intrusion; although this seems probable, as all show 

similar alteration.

The dikes are sharp-walled, yet they were intruded 

before the introduction of the solution that altered 

both anorthosite and dikes. These solutions were 

able to penetrate throughout the anorthosite, producing 

marked mineralization, even at a distance from channels of introduction. These relations show that the 

dikes were intruded after the anorthosite became rigid 

enough to fracture, but they suggest a porosity in the 

enclosing anorthosite, due to incomplete consolidation, 

probably incomplete cooling, and introduction of the 

dikes soon after the anorthosite was formed.

The ferromagnesian dikes exposed in the region are 

clearly not an adequate source for the solutions whose 

replacement products indicate a ferromagnesian source. 

This indicates the presence in depth of a ferromagnesian 

rock and suggests its relationship with the hypabyssal 

dikes—that is, the anorthosite, the dikes, the parent 

abyssal rock of which they are the offshoots, and the 

escaping solutions are all believed to be genetically 

related and to have been intruded without any great 

time intervals. This accords with the widely accepted 

view that anorthosites and the commonly associated 

ferromagnesian rocks are differentiates from the same 

parent magma, although not all are agreed as to the 

mechanism of that differentiation.

DISSEMINATED MINERALS

The rutile produced in the Roseland district is 

recovered from disseminated deposits in granulated 

anorthosite, in which it occurs in association with 

ilmenite and a varied group of other secondary minerals. 

The disseminated ilmenite is most abundant in the 

lenses of ferromagnesian minerals, close to them or to 

fracture planes that cut the anorthosite. It is also 

abundant in the injection gneisses, along the borders of 

the andesme anorthosite, in the gray oligoclase anorthosite, and in the ilmenite nelsonite discussed on pages

20-22. Ilmenite commonly forms very irregular grams 

or lenslike areas, which reach a maximum length of 

about 1 centimeter, as shown in plates 13, 14, and 15.

Rutile is also associated, although less closely, with 

the zones of fracture. Small amounts are present in 

the ferromagnesian lenses and close to them, where 

ilmenite is the dominant titanium mineral; but rutile 

becomes dominant only at some- distance from such 

zones. Thus ilmenite and rutile show zonal relations 

to each other.

The proportions of disseminated rutile in the mines 

of the American Rutile Co. are extremely variable but 

average only a few percent. The mode of occurrence 

of the rutile is illustrated in plates 1 and 11, where it 

shows as nearly equidimensional grains that have the 

same general form as the ilmenite and that range from a 

small fraction of a millimeter to 10 millimeters in diameter. The microscopic needles of rutile enclosed in 

quartz are described on page 11 and illustrated in 

plate 5, A. In the mine of the American Rutile Co. 

granular rutile of visible size is commonly absent in the 

blue quartz, but on the Bryant farm numerous masses 

of float quartz contain rutile in scattered grains that 

reach several millimeters in diameter. In the same area 

other masses of blue quartz contain disseminated grams 

and aggregates of apatite. (See pi. 12, B.)

Most of the ilmenite, rutile, and associated apatite 

grams are unfractured, and in the few crystals where 

slight fracturing has occurred displacement of the fragments is at most slight. Many specimens in the 

transition zone between ilmenite and rutiJe show that 

rutile has been replaced by ilmenite, as illustrated in 

plates 18, A, B, and 19, D. In some specimens narrow, 

irregular ilmenite borders surround rutile crystals, 

other grains of rutile are cut by numerous fractures 

along which ilmenite has formed, and some contain 

several small isolated residual areas of rutile enclosed 

in ilmenite. Ilmenite is commonly surrounded by a 

narrow zone of the alteration product ]<mcoxene as 

shown in plate 18, B, C, and less commonly leucoxene 

has formed around rutile. Sphene seems to have 

formed at about the same time as the leucoxene but 

largely by direct replacement of feldspar, although 

some appears to be an alteration product of rutile.

Apatite is typical of the various types of nelsonite 

but also occurs locally in ores of the disseminated type 

and the border facies, where it commonly forms crystal 

aggregates, rather than isolated grains. The mode of 

occurrence of small lenses of nelsonite hi feldspar in the 

mine of the American Rutile Co. is discussed on page 21 

and pictured in plate 12, A. Apatite aho occurs in 

some of the ferromagnesian lenses, where it forms 

irregular masses that cut through or send projections 

far into single crystals of hypersthene. (f^e pi. 9, A.}

Beginning with the formation of titanium minerals, 

but probably continuing after them, a group of secondary silicates was deposited. Like the titanium min-
OKIGIN OF THE BOCKS AND MINERALS 19

erals, they show a zonal relation to shear zones, and al] 

are the result of the replacement of feldspar. The 

thoroughly granulated portions of the anorthosite, 

which commonly show evidence of intense replacement, 

contain microscopic disseminated grains of micas, 

actinolite, tremolite, clinozoisite, and more locally 

titanium minerals. These grains may be rather uniformly scattered through feldspar, form irregular 

swarmlike areas, or occur in zones along minor fractures. 

(See pis. 2, 3, and 4.) The feldspar matrix around 

them is fresh and unaltered. The secondary minerals 

commonly form mixed aggregates, but one or more of 

them may predominate over the others. Biotite occurs 

only near ferromagnesian lenses or ilmenite and is 

associated with actinolite. Thus ilmenite, biotite, and 

actinolite (minerals carrying essential iron) are localized 

near feeding fractures but are commonly associated 

with low-iron sericite and clinozoisite. Sericitic muscovite, tremolite, and clinozoisite commonly occur 

together at greater distances from feeding fractures, 

and sericitic muscovite and clinozoisite are present 

throughout the mass. Some of the feldspar contains 

small numbers of minute rutile grams somewhat similar 

to those in the rutilated quartz. It is not clear when 

these formed, but localized occurrence and absence from 

ungranulated feldspar suggest that they are a product 

of replacement.

FERROMAGNESIAN LENSES

Numerous roughly parallel lens-shaped masses of 

ferromagnesian rock occur in parts of the quarry of the 

American Rutile Co.'s mine. These are very irregular 

in form and range from mere stringers 1 millimeter or 

less in width to lenses that are rarely more than 10 or 

15 centimeters wide. Some are sharp-walled, but others 

grade out into areas of disseminated minerals in anorthosite. The relation of the ferromagnesian lenses to 

fracture zones is shown in plates 6, 7, and 8, although 

nearly all specimens show the same relation more or less 

clearly. The major fractures along which replacement 

has been most intense are roughly parallel and are 

occupied by coarse-grained clinohypersthene that has 

been partly altered to a fibrous aggregate of amphiboles. 

(See pis. 6 and 9.) Another set of small, roughly parallel fractures makes an angle of about 45° with the major 

ones. The portions of these closest to the larger lenses 

tend to widen and are filled with pyroxenes and their 

alteration products, but the narrower portions are 

filled with biotite, as shown in plates 6 and 7.

A pyroxene, probably clinohypersthene, also formed 

lenses and irregular masses in the border facies of the 

anorthosite at Rose Mills, as illustrated in plate 16, B. 

This material, however, has been completely altered to 

a compact fibrous aggregate of hornblende crystals. 

Hornblendes, probably derived from orthorhombic

pyroxene, forms masses up to several feet in diameter in 

partly kaolinized feldspar, on the Bryant farm on Alien 

Creek, near the south border of the anorthosite body. 

There are two possible theories of formation cf the 

lenses: they may be considered primary products of 

differentiation, or secondary products resulting from 

replacement. The anorthosite mass is believed to have 

been formed by segregation of crystal fractions, with 

the lighter feldspar tending to float and the ferromagnesian minerals to sink. Aggregates of these sinking 

crystals may have been caught in parts of the largely 

crystalline anorthosite and introduced together with it 

during intrusion. This would tend to drag the ferromagnesian aggregates out into lenslike groups. That is, 

the pyroxene lenses may be assumed to be products of 

segregation. The shearing along these lenses jmy be 

explained as being later than the formation of the pyroxene and connected with the introduction of solutions 

that altered the pyroxenes to hornblende.

This segregation origin of the pyroxene lenses i^1 believed to be improbable for the following reasons. Their 

distribution seems to be in general controlled by f Hear 

zones that have the same direction hi the part of the 

quarry where the lenses occur and hi the more extensive 

parts where they are absent. However, mineralization 

has occurred along all the shear zones of the quarry 

and seems to have differed only in being more intense 

or in representing a little earlier stage in the clinohypersthene lenses. Thus the direction of shear was 

probably not controlled by the direction of pre-existing 

clinohypersthene lenses but preceded their introduction. 

Some of the lenses are near but not directly in fhear 

zones, and many have the irregular form that commonly 

characterizes replacement. The large masses of ^inohypersthene show little or no granulation. Small fingerlike offshoots of clinohypersthene were formed in the 

Echelon fractures that make an angle of about 45° with 

the major ones. Very irregular or badly corroded r.reas 

of feldspar along the border or within the clinohypersthene masses are partly replaced remnants of anorthosite. The large irregular masses of hornblende OK the 

Bryant farm are made up of coarse crystals that p enetrate the feldspar in all directions, giving shapes that 

would not have survived, had they been present during 

intrusion. These relations seem to accord with the 

theory of replacement by clinohypersthene better than 

with that of primary products of crystallization.

Three distinct stages were represented in the formation 

of the clinohypersthene-lens facies of anorthosite. The 

first was the formation of the purely feldspathic anorthosite, the second the introduction of clinohypersthene by 

replacement of the anorthosite, and the third the formation of all the other secondary minerals, including 

quartz, apatite, ilmenite, rutile, amphiboles, sulfides, 

and micas. There are evidences of a mineral sequence
20 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

within the third group, but they are believed to be 

closely related genetically, and there was no doubt 

much overlapping in their time of formation.

The mutual relations of the various minerals of the 

ferromagnesian lenses that cut the anorthosite are as 

follows: The clinohypersthene shows various degrees 

of alteration. In some specimens secondary amphiboles have formed only narrow films along the borders 

of crystals, or along small crosscutting veins, as shown 

in plates 6 and 9, B. Commonly alteration has occurred 

along the cleavage planes in clinohypersthene, so that 

the rock is now composed of alternating lenses of that 

mineral and amphiboles (see pi. 9, A), but in other 

parts alteration to a fibrous aggregate of amphiboles 

has been almost complete. Ilmenite is associated only 

with minerals that have invaded the clinohypersthene 

crystals and nowhere occurs in unaltered portions. 

(See pis. 14, D, and 17, A, B, C.) Most commonly 

ilmenite and amphiboles occur together in these veins, 

but, as shown .in plate 17, quartz and ilmenite have 

formed together in cleavage planes in clinohypersthene. 

On the other hand, plates 5, B, and 8 show that amphiboles have replaced quartz, and this seems to be the most 

general relation. Sulfides occur together with amphiboles in veins cutting clinohypersthene. (See pi. 9, 

B.} Micas did not form directly within the clinohypersthene masses but along their borders and in the small 

echelon fractures associated with the major ones. 

Biotite was formed abundantly in the injected schist at 

Rose Mills. Biotite has been partly altered to chlorite.

The relations just described indicate that the andesine 

of the anorthosite preceded all other minerals and was 

followed by clinohypersthene, which in turn was 

followed by all the other minerals except a small part 

of the quartz. Most of the quartz preceded apatite, 

ilmenite, and amphiboles. Biotite and clinozoisite 

were probably formed at about the same time as amphiboles. An exception to this order is that part of the 

ilmenite and amphiboles and part of the ilmenite and 

quartz were formed together.

NELSONITE

Some of the nelsonite bodies in the Roseland district 

are so poorly exposed that it is not possible to make 

detailed studies of the mineral relations and to reach 

definite conclusions about their mode of origin. Others 

of the "hard ore" type are composed almost wholly of 

apatite and ilmenite and do not show many significant 

relations. However, many of the nelsonite bodies, or 

parts of bodies with a more varied mineral content, 

show relations that seem to indicate very clearly the 

mode of origin.

Replacement processes seem to have been the controlling factor in the formation of nelsonite. Even the 

nearly pure apatite-ilmenite nelsonite shows evidence 

of a sequence of minerals, as the apatite is rounded and 

embayed, and ilmenite veinlets commonly cut apatite

grains, as shown in plates 14, A, 17, D, and 18, C, D. 

Biotite is present in varying amounts in nearly all 

types of nelsonite, and in all of these its presence as 

veins cutting apatite, ilmenite, or rutile (see p1 . 18, C, D) 

is evidence of its secondary origin. The replacement 

of rutile by ilmenite shows that at least part of the 

ilmenite is secondary. Veinlets of magnetite in ilmenite 

show the late introduction of at least part cf the iron.

The minute veinlets of quartz and ilmenite in clinohypersthene, illustrated in plate 17, afford excellent 

evidence of the secondary character of the ilmenite, as 

they follow cleavage planes in clinohypersthene and 

hence are later than that mineral. The invasion of 

clinohypersthene by ilmenite is shown in plate 14, D. 

A similar relation is shown by veinlets of hornblende 

and ilmenite in the cleavage planes in clinohypersthene.

The most informative of 'the nelsonite bodies of 

complex mineralogy and abundant silicate minerals is 

that being mined by the Southern Mineral Products 

Corporation on the Tye River. Near the footwall of 

this body are numerous small lenses of anorthosite, and 

many small lenses of nelsonite cut the anorthosite 

country rock beyond the main body of nelsonite. The 

nelsonite shows a marked schistosity that is parallel 

to the shear zones in the anorthosite along which these 

small lenses of anorthosite have been formed, as illustrated in plates 13 and 15. The lenses in the anorthosite are typical andesine anorthosite and show various 

degrees of replacement. One large body, novr removed, 

contained a few percent of apatite and ilr^enite .but 

was not essentially different from the. anorthosite of 

the disseminated deposits. It contained the usual 

secondary minerals, including tremolite, sericite, and 

clinozoisite disseminated in antiperthitic andesine. On 

its border this mass graded over into Kotite-rich 

nelsonite.

A small lens of anorthosite from the central part of 

the anorthosite is composed of nonperthitic andesine 

that has been partly replaced by actinolite, sericite, 

and clinozoisite, with a few completely altered augen 

similar to those discussed in the next paragraph.

The fresh hornblende nelsonite illustrated in plate 

13, D, is composed of small augen surrounded by hornblende in parallel wisps. A few of these augen are 

andesine which has remained unreplaced or only partly 

replaced, but most of them are fine-grained aggregates 

composed of secondary albite, hornblende, and clinozoisite. The only difference between the two specimens 

just described is that the nelsonite was very closely 

sheared, permitting the easy access of solutions and 

very thorough replacement, while the anorthosite lens 

escaped this close shearing. Other lenses nearer the 

contact are intermediate between these two in the 

degree of replacement.

Material of another type'that shows tl o relation 

between nelsonite and anorthosite was obtained from 

the dumps of the old General Electric Co.'s mine and
ORIGIN OF THE ROCKS AND MINERALS 21

is shown in plate 11. The lighter-colored portions near 

the bottom and the right side and isolated masses 

throughout the specimen are altered andesine, which 

contains abundant, finely disseminated actinolite, muscovite, and clinozoisite grains. Near the right side of 

this specimen an irregular zone of dark-gray color 

peppered with white spots is typical granular nelsonite, 

composed of apatite and rutile. To the left of this 

zone, at the top, a very irregular veinlike area extending 

into the center of the specimen is dark-gray material 

that is almost pure apatite. This apatite zone in turn 

grades into a very irregular zone that sends fingerlike 

areas of apatite far into feldspar, which has been partly 

altered to clmozoisite and which shows as medium 

light-gray veinlets and irregular patches. Numerous 

light-gray veinlets extend throughout the specimen 

where clmozoisite has been formed along fractures. 

Small isolated areas of rutile (black) or rutile and apatite together are scattered through the specimen, and 

some of them occur entirely within andesine masses. 

Near the extreme upper side is an irregular residual 

area of highly altered feldspar enclosed in a nearly 

pure mass of apatite and rutile. Within this area are 

scattered nests of apatite and rutile. In this specimen 

the mineral relations are shown with great clearness and 

present an almost ideally perfect example of replacement.

Several small veins of nelsonite cut the anorthosite in 

one part of the mine of the American Rutile Co., and 

the relations of one of these are shown in plate 12, A. 

The light-colored portion on each side is much-altered 

andesine, which is cut by a vein that is dominantly 

apatite but has ilmenite concentrated near the borders. 

Near the bottom of the specimen and extending 

diagonally upward from the lower right-hand corner 

of this vein is a branch veinlet of apatite and ilmenite, 

which has formed along a fracture that makes an angle 

of about 45° with the major fracture. Numerous dark 

areas throughout the specimen represent ilmenite and 

a little associated apatite, which have replaced feldspar.

Small fragments of amphibolite nelsonite from the 

Bryant farm .on Alien Creek are composed largely of 

pyroxenes and amphiboles and lesser amounts of 

ilmenite and apatite but contain remnants of anorthosite, as shown in plate 13, A, B, and C. These remnants occur as elliptical or augenlike areas that are 

commonly only a millimeter or two in length. They 

show extreme alteration and are bordered by conspicuous reaction rims of secondary minerals. The relations 

are similar to those shown in the hornblende nelsonite 

from the mine of the Southern Mineral Products Corporation, represented in plate 13, D, and differ only in 

that in the latter replacement is a little less complete. 

In some specimens the reaction rim is a very finegrained aggregate of colorless garnet around feldspar, 

as shown in plate 13, C. Augenlike areas of garnet are 

abundant and probably represent replaced anorthosite. 

The pyroxene forms phenocrystlike areas, which have

commonly been altered to fibrous hornblende, although 

some are still almost unaltered. The relations of 

amphiboles and biotite indicate that they are all 

secondary. The quartz occurs hi small lenses and 

appears to be later than pyroxenes, although itr replacement by amphiboles and biotite indicates that it 

is an early mineral. Apatite forms rounded grains 

that tend to be distributed in zones. Ilmenite occurs 

in fine grains, some of which are dustlike and are 

distributed in wisplike zones and lenses that give the 

rock a schistose habit, as shown in plate 13, A. The 

zones cut across crystals of pyroxene and apatite, 

showing that they are later than these minerals.

In the rutile nelsonite on the Giles property the 

secondary minerals that have developed on the immediate contact with enclosing rock are dominantly 

sericitic muscovite, with very small amounts of chlorite 

and clinozoisite. There is a little coarsening of the 

grain size of sparse enclosed muscovite, but in general 

the sericite on the immediate contact is not different 

from that which has formed throughout the anorthosite body. Also there has been no alteration or recrystallization of antiperthitic feldspar except for this 

formation of sericite. Thus there is no indication of 

high temperatures at the contact of rutile nelsonite 

with enclosing rock, and all the alteration is of the type 

characteristic of hydro thermal processes.

The gneissic country rocks, the border facies of the 

anorthosite, the oligoclase anorthosite, the lenses of 

hypersthene hornblende masses on the Bryant farm, 

the intrusive dikes, and the nelsonite amphibc Utes 

contained original iron-bearing minerals. Where these 

were invaded by titanium-bearing solutions the local 

supply of ferrous iron permitted the direct formation 

of ilmenite.

Watson and Taber 30 have pointed out that the rutile 

nelsonite is confined to the anorthosite, whereas that 

in the country rock is invariably ilmenite nelsonite. 

On the other hand, in the disseminated deposits ilmenite 

occurs hi and close to the shear zones that acted as 

feeders, but within short distances of such feeders preilmenite ferromagnesian minerals are absent and rutile 

becomes dominant. These relations show that the 

incoming solutions were deficient in iron, so that the 

ilmenite zones within the originally iron-free anorthosite 

were limited to close proximity to feeding channels, 

and away from these channels the nearly iron-free 

rutile was formed. The replacement of rutile by ilmenite and the direct formation of ilmenite where 

local supplies of iron were available show that ilmenite 

tended to be formed in preference to rutile wherever 

adequate ferrous iron was available.

In the rocks where a local supply of iron was absent, 

it is evident that in the intermediate zone rutile was 

formed first and was later more or less completely 

replaced by ilmenite. However, definite evidence is

3« Watson, T. L., and Taber, Stephen, op. cit. (Bull. III-A), p. 101.
22 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

lacking for the inner zones where only ilmenite is now 

present. Here, for all that can be directly observed, 

ilmenite may have been formed as the primary titanium 

mineral. On the other hand, rutile may have been 

formed first and the process of replacement has gone 

to completion. However, the partial replacement of 

rutile by ilmenite and the formation of magnetite in 

minute fractures in ilmenite prove a sequence in the 

composition of the mineralizing solutions, with titanium, 

at least in part, preceding ferrous iron and iron persisting after titanium was greatly diminished or exhausted.

Solutions may possibly have carried both titanium 

and iron, and as the first wave penetrated the granulated feldspar the iron was quickly abstracted in the 

formation of iron-bearing minerals, after which rutile 

was formed. With continued flow of solutions the 

zone of depletion in iron may have gradually moved 

outward, so that iron-bearing minerals were formed 

farther and farther from the feeders. On this assumption, when solutions not yet impoverished in iron came 

into contact with rutile, it was replaced by ilmenite, 

the varying iron content of a single wave of solutions 

being the controlling factor in determining whether 

ilmenite or rutile formed. On the other hand, the 

most probable mechanism of segregation and transportation of titanium and iron and the sequence of 

their deposition seem to make an early vapor phase for 

titanium and a later liquid hydrothermal stage for 

ferrous iron the most probable assumption. (See 

pp. 33-37.)

A very general assumption has been that the titanium 

deposits were formed by a process of magmatic segregation. This assumption was perhaps based on the 

hard ores of the nelsonite that show the least direct 

evidence of replacement. However, it is obvious that 

any explanation of nelsonite must apply to all types, 

including the amphibolite-nelsonite. The presence of 

a large proportion of replacing minerals shows that the 

nelsonites containing them were not formed by a single 

intrusive process. It may be assumed that the earlier 

minerals (ilmenite, rutile, and apatite) were the result 

of magmatic segregation and that secondary minerals 

such as biotite were the product of later hydrothermal 

processes. Numerous occurrences show that ilmenite, 

rutile, and apatite have themselves invaded older 

minerals and indicate that all the minerals of nelsonite 

have been formed by the replacement of anorthosite.

Much of the nelsonite of the Roseland district contains a group of silicate minerals that are identical with 

those associated with the disseminated deposits. The 

nelsonite bodies of dikelike or veuilike character are 

intrusive into the anorthosite and so are definitely later 

than the anorthosite. If the disseminated deposits are 

magmatic they must have been formed together with 

the anorthosite. An origin of both types of deposits by

magmatic segregation implies two distinct periods during which titanium mineralization was active; the two 

could not have been formed together by magmatic 

segregation. On the other hand, magmatic r^gregation 

of the nelsonite occurring concomitantly with replacement hi the anorthosite and the formation of its disseminated minerals implies two distinct modes of origin 

for like suites of minerals. Perhaps neithe** of these 

alternatives is impossible, but they seem very improbable.

SUMMARY OF EVIDENCE OF ORIGIN

The preceding sections have described the various 

rock types and mineral relations that indicate a secondary origin for the titanium and associated minerals, 

and this evidence may now be briefly summarized.

The titanium and associated minerals are absent in 

the ungranulated primary feldspar and are confined to 

the granulated portions and so were introduced after 

the anorthosite crystallized. Ilmenite has replaced 

amphibole-pyroxene masses that have themselves replaced anorthosite. The secondary minerals show an 

erratic distribution and are most abundant in or near 

fractures capable of acting as feeders for incoming 

solutions. Swarms of minute minerals have formed 

entirely within single grains of feldspar, a relation commonly resulting from secondary reactions. The ilmenite, rutile, and apatite are ungranulated, although 

occurring hi thoroughly granulated rock. The associated actinolite, tremolite, sericitic muscovHe, garnet, 

and clinozoisite are a typically hydrothemal suit of 

minerals, clinozoisite and garnet probably being always 

secondary. The localization of iron-bearing minerals, 

with ilmenite, biotite, and actinolite near shear zones 

and nearly iron-free rutile and magnesian tremolite at 

greater distances from feeders, presents a zonal relation 

indicative of formation by solutions. The formation 

of much of the ilmenite was controlled by local supplies 

of iron, and rutile was developed only wher? iron was 

absent, indicating mineralization during alteration of 

the enclosing rocks.

Ilmenite and the same group of associated minerals 

have been formed within the pre-anorthosite country 

rock near the contact. Abundant sphene formed hi 

quartz monzonite at least a mile from the contact. The 

dike rocks that intrude the anorthosite contain ilmenite and clinozoisite. Ilmenite and quartz, or ilmenite 

and hornblende, have formed small veinlets hi cleavage 

planes in clinohypersthene and so have invaded that 

mineral. Two distinct types of deposits s*,em inconsistent with a pyrogenic origin, but not wit! a replacement origin.

The mutual relations of the minerals of the Roseland 

region are shown in the accompanying table, which is 

arranged to show the succession of the minerals and the 

evidence pointing to this succession.
Paragenesis of minerals from the Roseland titanium district, Virginia

[ The successive minerals are shown in the box beading. To find the relation of any mineral, read the name underlined by the heavy line that runs across the table, follow the horizontal line, 

read the name of the mineral showing that relation. Follow the horizontal line to the left for minerals earlier in the mineral sequence, and to the right for later minerals. For example, apa

andesine (earlier) and is cut by veinlets of rutile, ilmenite, amphiboles, and micas (later). Blank spaces are left where relations are not evident.]

ANDESINE

ANDESINE

Occurs in shear 

zones in

Forms veins in

Forms veins in

Occurs in sheared 

portions of

Occurs in sheared 

portions of

Form veins in and 

replace

Form veins in and 

replace

Forms veins in and 

replaces

CLINOHYPERSTHENE

Cut by veins of

CLINOHYPERSTHENE

Forms veins in

Forms veins in

Forms veins in

Forms veinlets in

Form veins in, and 

alteration product of

Alteration product of

QUARTZ

Cut by veins of

Cut by veins of

QUARTZ

Forms veins in

Forms minute 

crystals in and 

occurs in veinlets 

with

Occurs in veinlets 

with

Form veins in 

and replace

Replace

Forms veins in

APATITE

Cut by veins of

Cut by veins of

Contains veins 

of

APATITE

Forms veinlets 

in

Forms veinlets 

in

Form veinlets in

Foim veinlets in

RUTILE

Granulated andesine contains

Cut by veins of

Contains minute 

crystals and 

veins of

Cut by veinlets 

of

RUTILE

Replaces

Form veinlets in

ILMENITE

Granulated andesine contains

Cut by veins of

Cut by veins 

containing

Cut by veinlets 

of

Replaced by

ILMENITE

Occur in veinlets with

Form veinlets in

AMPHIBOLES

Contains veinlets and 

disseminated crystals of

Altered to

Formed together 

with, and cut by 

later veins of

Cut by veinlets of

Cut by veinlets of

Occurs in veinlets 

with

AMPHIBOLES

Associated with

Associated with

Con

nate

Sur

reac

Cut 

Cut 

Cut 

Ass

Ass

BELATED TITANIUM DEPOSITS 23

RELATED TITANIUM DEPOSITS

ST. URBAIN, QUEBEC

The titanium deposits of the St. Urbaiii area, 

Charlevoix district, Quebec, present marked similarities 

to those of the Roseland district of Virginia. Mawdsley 31 describes the area as follows:

The small anorthosite boss within the St. Urbain map area 

is on the southeast margin of the belt of anorthosite masses 

extending through Quebec. This boss is oval in shape, with a 

major axis about 18 miles long and a minor axis of 9 miles. 

The major axis has a north and south direction and passes close 

to St. Urbain, which lies 3 miles within the anorthosite body. 

This ovoid area, except for a few deposits of ilmenite, is underlain, so far as known, only by anorthosite. The anorthosite 

varies in composition from place to place and ranges from a rock 

essentially composed of andesine (AbTo-esAngo-ss) to one essentially composed of labradorite (Ab44_35An56-65). * * *

Large plagioclase crystals characterize the andesine anorthosite, and in many places the labradorite anorthosite appears 

formed of crushed large feldspars. * * *

A marked feature of the contact between the anorthosite and 

the granite-diorite batholith is the foliated zone which follows 

the contact.

Several of those who have studied the deposit have 

concluded that the ore minerals were introduced as 

a magma. Osborne 32 says, "The field and laboratory 

work show that the ores are not magmatic segregations 

but are magmatic injections." Mawdsley 33 says, 

"It is the writer's opinion that they [ilmenite deposits] 

are magmatic in origin and were intruded as a liquid 

magma of essentially their present composition." On 

the other hand, Gillson 34 concludes that they have 

been formed by hydrothernial processes. He says:

Horses of barren anorthosite are a common feature of all the 

ore deposits. They are of varying size and shape and in most 

cases have sharp boundaries, as do also the ore bodies themselves 

against their walls. All the horses show considerable evidence 

of hydrothermal action. * * *

The gangue minerals are the andesine of the original anorthosite, which is the only primary rock mineral found in any quantity 

in any of the slides examined, and the following minerals, which 

formed in the old rock by replacement: A mica close to phlogopite, apatite, tourmaline, rutile, sapphirine, quartz, spinel,

zoisite, chlorite, sericite, serpentine, carbonate and zeolites.

* * *

The author concludes that the ores were formed by replacement in the already solid anorthosite and were deposited from 

solutions, either gaseous or liquid, which soaked through the 

rock. The ores are not pyrogenetic or orthotectic but were 

related to the anorthosite, in the sense that the solutions came 

from a reservoir in depth with which the magma that formed 

the anorthosite had previously been connected. The formation 

of the ores then belongs to the same general magmatic period as 

does the anorthosite, and the latter was still hot when the ore 

was formed. The following points can be tabulated as proving 

this conception:

3i Mawdsley, J. B., St. Urbaiii area, Charlevoix district, Qubec: Canada Qeol. 

Survey, Dept. Mines, Mem. 152, Qeol. ser., no. 133, pp. 18, 19, 29, 1927.

3? Osborne, F. F., Certain magmatic titaniferous iron ores and their origin: Econ. 

Geology, vol. 23, p. 921, 1928.

33 Mawdsley, J. B., op. cit., p. 46.

« Gillson, J. L., Genesis of the ilmenite deposits of St. Urbain, County Charlevoix, 

Quebec: Econ. Geology, vol. 27, pp. 554-577, 1932.

The ores are related to definite structural lines that developed 

after the solidification or approximately entire solidification of 

the anorthosite. * * *

The ores occur in many places in narrow veinlets or stringers 

that are many feet long in places, and in microscopic section can 

be seen to have followed along cracks and cleavage lines in other 

minerals, and large masses of old rock exist with disseminated 

ore in them. Such features could not have formed from a 

magma unless it had been an exceedingly tenuous one.

The ores have all the characteristics of replacement deposits. 

A definite paragenesis of minerals can be observed, which shows 

a sequence from a higher-temperature period to a lower-temperature period and indicates a long period of deposition. * * *

The writer believes that the large masses of disseminated ore 

are an especially firm proof of a deposition of the ore by solutions, once the conception of the contained ilmenite having 

formed by replacement is established.

This disseminated ore is original anorthosite, more or less 

replaced by phlogopite and ilmenite and their associates ard with 

the old feldspar riddled by chlorite and zeolites. The massive 

ore differs from the disseminated ore only in the degree of replacement. The horses are simply unreplaced remnants.

The paragenesis, so far as it could be established, was oligoclase, phlogopite; rutile, apatite, sapphirine, spinel, ilmenite, 

and probably quartz; sulfides, serpentine, chlorite, carbonate, 

and zeolites. The paragenetic sequence is considered to have 

been continuous and overlapping. Whether the emanations 

were gaseous or liquid is not known; probably they started out 

in a gaseous form and were completed as a liquid.

The conclusions of Gillson about the St. Urbain ores 

agree in all essential particulars with those of the 

writer about the ores of the Roseland district of Virginia—that is, in both areas the disseminated ores hi 

the anorthosite as well as the segregated ores have 

been formed by hydrothermal replacement of anorthosite, and in both areas the ores are associated with 

a typically hydrothermal group of secondary mirerals.

MAGNET COVE, ARKANSAS

The Magnet Cove district of Arkansas, which has 

become a producer of titanium ores, was visited ly the 

writer in November 1937, in company with IT. D. 

Miser and W. T. Schaller, of the United States Geological Survey, in order to compare the deposits with 

those of Virginia. Here one deposit is being actively 

mined, and prospecting has shown the wide occurrence 

of titanium ores at other places.

Magnet Cove has long been noted for its rare rock 

types and interesting minerals. These have been 

described in great detail by Williams 3S in a report 

that is one of the classics of petrographic literature, and 

later by Washington.36 The minerals have been discussed by many writers, and a few of the more rscent 

reports are those by Landes 37 and by Landes, Parks, 

and Scheid.38

s« Williams, J..F., Geol. Survey Ann. Rept. Arkansas for 1890, vol. 2, fr>. 1-432, 

1891.

s» Washington, H. S., Igneous complex of Magnet Cove, Arkansas, G"ol. Soc. 

America Bull. vol. 21, p. 399,1900; Thefoyaite—ijolite series, Magnet Cove, Ark., a 

chemical study of differentiation: Jour. Geology, vol. 9, p. 611,1901.

3' Landes, K. K., A paragenetic classification of the Magnet Cove minerals: Am. 

Mineralogist, vol. 16, pp. 313-326, 1931.

38 Landes, K. K., Parks, Bryan, and Scheid, V. E., Magnet Cove, Ark.: 16th 

Internat. Geol. Gong. Guidebook 2, pp. 101-112, 1932.
24 TITANIUM DEPOSITS OF NELSON AND AMHEKST COUNTIES, VIRGINIA

The rocks of the Magnet Cove region are sedimentary, being shales, sandstones, and novaculite (a 

chertlike rock composed wholly of silica). The shales 

have been metamorphosed into slates during the intense 

folding that the region has undergone. The rocks are 

of Paleozoic age, and folding and metamorphism are 

believed to have taken place near the end of the Paleozoic era. The igneous rocks are of Cretaceous age 

and are subsilicic, being characterized by nepheline 

and in one of the dominant types by abundant pseudoleucite. These igneous rocks form a nearly continuous 

and roughly circular rim within which is a basinlike 

area about 2 miles' across known as Magnet Cove. 

Within this area exposures are sparse and discontinuous, but highly altered slate, novaculite, igneous rocks 

that have undergone marked secondary changes, and 

a very coarse grained calcite rock containing interesting secondary silicates have been recognized. Outside 

the basin, especially on the east and northeast, the 

sedimentary rocks show marked changes caused by 

magma tic solutions.

Titanium ores are being produced by the Titanium 

Corporation, of Malvern, Ark., from an area lying 

about IK miles northwest of Magnet post office. Here 

the rocks are highly altered and deeply weathered, but 

the essential relations can be observed in the open cuts 

resulting from steam-shovel operations. The material 

in which the ores occur is a clastic aggregate composed 

of exceedingly varied rock types. This material is 

cut by dikes of ferromagnesian rocks, of which some 

are altered but others are fresh below the zone of 

weathering. The clastic material is made up of minor 

amounts of metamorphosed novaculite and slate, intermixed with igneous rock fragments—that is, it is a 

volcanic agglomerate. These fragments range in size 

from finely comminuted material to blocks 10 feet or 

more across. In much of the area exposed by mining 

operations, the fragments are set in a matrix that is 

now a fine-grained white clay. Microscopic study of 

the igneous material shows many rock types, only a 

few of which need be enumerated. The least-altered 

is a nearly pure orthoclase rock; others are partly 

altered plagioclase rocks and several types contain 

biotite. All show varying degrees of alteration to a 

beidellitelike clay mineral and to kaolinite. The white 

matrix shows well-preserved glassy volcanic tuff structure, although now completely altered to the clay 

minerals beidellite and kaolinite—that is, the material 

is now a bentonite. Thus the heterogeneous mixture 

of sedimentary and igneous materials is clearly pyroclastic in origin and was, no doubt, derived from an 

explosive volcanic vent in the immediate vicinity. 

Explosive volcanic activity has previously been recognized in southern Arkansas and in widely distributed 

localities in the Coastal Plain region 39 but not before

*• ROES, C. S., Miser, H. D., and Stephenson, L. W., Water-laid volcanic rocks of 

early Upper Cretaceous age in southwestern Arkansas, southeastern Oklahoma, and 

northeastern Texas: U. S. Geol. Survey Prof. Paper 154-F, pp. 175-202,1929.

at Magnet Cove, although Featherstonehau^h 40 suggested such a possibility in 1836.

The titanium minerals that occur here are dominantly 

rutile, with lesser amounts of brookite or pseudobrookite and a large proportion of so-called leucoxene. 

An X-ray examination of this material shows that it is 

anatase. Thus, the three crystal forms of TiO2, rutile, 

brookite, and anatase, have been recognized at Magnet 

Cove. These minerals occur in all types of ro^ks of the 

area, including the sedimentary rock fragments, and 

at least some of the intrusive dikes. Rutile se^ms to be 

most abundant in clastic materials and one of the most 

conspicuous occurrences is in the white Hntonitic 

matrix that was originally a glassy volcanic tuff. Here 

it forms irregular crystals as much as 2 or 3 m illimeters 

in diameter, which tend to occur in bunchy or streaklike 

friable aggregates that reach 2 or 3 centimeters in 

greatest dimension. The rutile is nearly black, much 

of it is coated with magnetite or encloses dustlike 

grains of magnetite.

Pyrite in crystals 1 centimeter in greatest diameter 

is abundantly associated with rutile in parts of the 

mine where operations have extended below the zone 

of oxidation, but above that zone the pyrite has been 

altered to limonite. It seems to be especially abundant 

in the material that was originally a glassy tuff.

All types of rocks making up the volcanic agglomerate 

contain abundant leucoxene, the amount reaching 50 

percent of the rock in at least one sample. Some of the 

leucoxene is an alteration product of sphere, whose 

form it retains, but most of it is in irregular r.reas that 

seem to have been formed directly by repT acement. 

Leucoxene has been formed in the vesicular cavities 

in nearly all glass shards and locally has completely 

replaced them. It fills fractures in orthoclase or albite 

grains and is abundant on the cleavage planes of biotite 

and its alteration products. A few grains of biotite 

have been completely replaced, with retention of the 

micaceous structure. Some fine-grained volcr.nic rocks 

have been very thoroughly replaced, only isolated 

areas of the original rock remaining. Sorre of the 

rocks are mixed with impurities, but others are pure 

masses of leucoxene 2 to 3 millimeters in diameter. 

Sharp-walled veinlets have been formed in many of 

the denser rocks.

The altered dikes contain smaller amounts of titanium minerals than the agglomerate, but titanite, rutile, 

and ilmenite are present and have been partly altered to 

leucoxene. Titanium minerals occur in association 

with pyrite in the altered dikes and were prcbably introduced into the dikes and agglomerates in the same 

manner.

The rutile in the sedimentary rocks and that associated with pyrite in the glassy tuffs affords evidence 

that they were introduced subsequent to the explosive

« Featherstonehaugh, G. W., Geological report of an examination nade in 1834 of 

the elevated country between the Missouri and Red Rivers: XT. S. C'^ologist Rept. 

to House of Representatives, p. 67, Washington, 1836.
RELATED TITANIUM DEPOSITS 25

activity that produced this heterogeneous aggregation 

of rock materials. Rutile and pyrite in essential 

amounts have never been recognized as primary constituents of volcanic glass, and even if they could so 

occur, they could not be present in unbroken grains 

several millimeters in diameter and in aggregates several centimeters in length, associated with tuff shards 

at most a few tenths of a millimeter in greatest dimensions.

The alteration of all types of rock to clay minerals 

has been very thorough and extended below the level of 

present operations and below the zone of oxidation. 

This indicates that the alteration was not due primarily 

to weathering but was a part of the process of mineralization. The abundant introduction of leucoxene, 

which seems to have accompanied the development of 

clay minerals, tends to confirm the liydrothermal origin 

of both clays and leucoxene.

The other occurrence of titanium minerals is in an 

area extending from the vicinity of Magnet post office 

northward and eastward for a mile or more. Prospecting has been most extensive about 1 mile north of 

Magnet, but similar mineralization seems to have 

occurred over an area of 1 square mile or more. The 

principal titanium mineral in this general area is brookite, a form of TiO2, but pseudobrookite, a paramorph 

of rutile after brookite, is probably also present. In 

much of the area the mineralized rock was originally 

novaculite, which shows varying degrees of modification 

by mineralizing processes. Unaltered novaculite has a 

dense, chertlike texture and is composed of nearly 

equidimensional quartz grains, a few hundredths of a 

millimeter in diameter, that are without crystal form. 

In a road cut at Magnet metamorphism has increased 

the size of the quartz grains until the novaculite resembles a fine-grained sandstone, and much of it has 

become so friable that it can be crumbled in the hand. 

Here brookite and quartz have been developed as very 

beautiful euhedral crystals as much as 1 centimeter 

in length that project into geodelike cavities that have 

been formed locally in the novaculite. About a quarter 

of a mile southeast of Magnet quartz crystals as much 

as 1 foot in length have been collected, and brookite 

crystals may be picked up on the surface of the soil.

In the area about a mile north of Magnet the surface 

is littered with masses of quartz rock that have undergone varying degrees of recrystallization. Much of 

this material is now composed of euhedral quartz 

crystals that are eommonly doubly terminated and 

coated with beautiful euhedral brookite crystals. The 

quartz crystals are commonly a few millimeters in 

length, but specimens have been observed that reached 

2 to 3 centimeters. The brookite crystals are in 

general about 1 millimeter in diameter and rarely 

exceed 2 or 3 millimeters. The masses of quartz 

associated with brookite are as a rule extremely porous 

and have seemingly lost as much as half their volume

during recrystallization from the originally dense ncvaculite. The origin of this material would not be evident were it not possible to trace all degrees of recrystallization from normal novaculite through that which 

has been slightly recrystallized to coarse-grained masses 

of vuggy quartz.

In the area 1 mile north of Magnet, prospect pits that 

have reached a depth of about 50 feet show a rubbMike 

mixture of rock fragments in a matrix of clay materials. 

The clay materials, at least locally, form more than half 

the rubblelike aggregate. Near the surface the clay is 

red as a result of weathering and oxidation, but in depth 

nearly white taeniolite, dickite, andkaolinite are present.

Even the small amount of material available from 

shallow prospect pits shows that the clay materials are 

at least in part the alteration products of volcanic ash. 

The rock masses of the rubblelike aggregate are dominantly quartz, but associated with these are smaller 

proportions of coarse-grained igneous rocks that were 

originally a nepheline syenite. The quartz is in part of 

the porous type above described and in part rounded 

boulderlike masses. The only remaining primary 

mineral of the igneous rock fragments is orthocla^e of 

the sanidine type.

The quartz and igneous rock masses in this area rorth 

of Magnet seem to represent fragments that were 

blasted loose from underlying beds and deposited 

together with volcanic ash during periods of violent, 

explosive volcanic activity. These materials were subsequently subjected to intense secondary minerslization. The orthoclase of the nepheline syenite fragments is only partly altered to claylike minerals, but 

areas of nepheline are completely altered. The volcanic ash has completely changed to clay materials, and 

quartz fragments have been partly replaced by taeniolite and dickite. The clay minerals recognized are 

kaolinite (Al2O3.2SiO2.2H2O); dickite, which has the 

same composition; and beidellite 9Al2O3.19SiO2 .6H20.- 

Na20. Taeniolite (KLiMg2Si4010 (F,OH) 2) is, at least 

locally, the most abundant secondary mineral. 41 

Brookite occurs in small grains throughout the rubblelike rock mass, and leucoxene is very abundant and 

shows the same evidences of secondary origin as at the 

rutile mine. The clay minerals kaolinite and beidellite 

are commonly the result of weathering processes, but 

more rarely have been formed in the presence of thermal 

solutions at moderate temperatures, probably at a late 

state in hydrothermal alteration. Taeniolite has been 

formed most abundantly by the replacement of novaculite boulders but to a lesser extent by the replacement 

of glass or of nepheline. In the area 1 mile to the north, 

as well as at Magnet,, the formation of brookite in 

novaculite clearly records the introduction of titanium 

into an originally pure quartz rock. The brookite 

crystals perched on quartz crystals resulting from the

«' Miser, H. D., and Stevens, K. E., Taeniolite from Magnet Cove, Art.: Am. 

Mineralogist, vol. 23, pp. 104-110,1938.
26 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

recrystallization of novaculite must also have been 

introduced by titanium-bearing solutions.

Thus two distinct areas in the Magnet Cove area show 

evidences of explosive volcanic activity, followed by 

mineralization that introduced titanium into originally 

titanium-free rocks. The large mineralized area, the 

introduction of so much new material, and the removal 

of great amounts of silica are evidences of large supplies 

of very active solutions.

Nearly 50 years ago Williams 42 described the introduction of titanium into sedimentary rocks and made 

the following statement:

The brookite crystals are found only upon quartz and sandstones of the region included within the cover proper or the belt 

immediately adjoining it near Magnet post office, or lying loose 

in the soil where they have been left by the disintegration of the 

sandstone. * * * That they are directly referable to the 

metamorphic action of the syenite is beyond a doubt, since 

nowhere else in this extensive series of sedimentary rocks have 

any such crystals been found. * * * The most plausible 

theory to account for the transformation of this element 

[titanium] from its original condition * * * in the syenite, 

to that of brookite * * * is that it was dissolved by the 

hot water and steam under pressure * * * and was recrystallized * * * when it reached the sandstone and quartz 

crystals. The titanium oxides may perhaps be considered as 

having been directly volatilized at the time of intrusion of the 

syenite and to have condensed as the dioxide directly, or else 

they may have been volatilized as the chloride of titanium and 

have been broken up on contact with the air and have formed the 

dioxide where it is now found.

Thus Williams clearly recognized this transfer of 

titanium from the parent igneous rock into the intruded 

rocks by hydrothermal or vapor phase processes.

Within the basinlike portion of the cove there is 

evidence of very thoroughgoing replacements that have 

introduced titanium, together with abundant other 

elements. Here both the titanium minerals (rutile 

and brookite) occur over wide areas, and locally perofskite (CaTiO3) has developed in crystals reaching 

1 centimeter on a side. The titanium garnets, melanite 

and schorlomite, with as much as about 21 percent of 

TiO2, are abundant in the rocks within the cove. However, exposures outside the area of active mining are 

too few and too discontinuous to permit an adequate 

study. In numerous areas the soil is littered with 

crystals of rutile, brookite, perofskite, magnetite, garnet, vesuvianite, nepheline, aegirite augite, apatite, and 

biotite and its alteration products vermiculite and 

chlorite. This float material probably represents only 

the minerals resistant to weathering and unfortunately 

tells but little about the exceedingly interesting geologic relations that must be concealed beneath the soil.

« Williams, J. F., Arkansas Geol. Survey Ann. Kept, for 1890, vol. 2, pp. 322-324 

1891.

PHYSICOCHEMICAL PROCESSES CONTROLLING 

MINERALIZATION

The geologic relations described in the foregoing 

pages present the basis for a consideration of the 

physicochemical processes that brought about the replacement of the anorthosite by titanium, phosphate, 

and silicate minerals. Such a consideration may be 

conveniently taken up in three parts—general theoretical background, segregation of mineralizing materials from the parent rock, and the chemistry of replacement. The segregation of materials preceded their deposition, which was by replacement of earlier minerals. 

It seems best to consider replacement first, because 

its results are directly observable, as those of segregation are not, and because the chemistry of segregation 

is in part indicated by the chemistry of replacement.

THEORETICAL BACKGROUND

STABILITY OF MINERALS

The solution, replacement, or alteration of a mineral 

in general implies that the mineral affected is unstable 

in its environment and that any new mineral formed is 

normally stable under that environment. It is recognized, however, that a mineral may persist almost 

indefinitely in an environment where it is potentially 

unstable—that is, in a metastable condition. It is 

also possible for a mineral of lower energy of formation 

to form first and later invert to the more stable form, 

or on the other hand, fail to invert—that is, remain in 

a metastable state. In other words, alteration or 

replacement of a mineral is in general evidence of its 

instability, but on the other hand absence of replacement is not necessarily evidence of stability.

Instability may be of several types. One is the result 

of an inherent instability that may be controlled by 

changes in temperature, pressure, or the chemical environment and is illustrated by the anorthite molecule 

discussed hi the following section. A mineral may be 

inherently stable and yet be replaced by ore of lower 

solubility, as where calcium carbonate is replaced by 

magnesium or iron carbonates. Also an inherently 

stable mineral may be replaced by another, as a result 

of the mass-action effect resulting from a marked change 

in the concentration of the ions making up the chemical 

environment.

A change in the physical state of the system—from a 

liquid to a gas or vapor phase—does not necessarily 

cause a change hi the stability relation, a? has been 

pointed out by Fenner 43 as follows:

ts Tenner, C. N., Pneumatolytic processes in the formation of minerals and ores: 

Ore deposits of the Western States (Lindgren volume), p. 80, Am. Inst. Min.Mte. 

,Eng., 1933.
PHYSICOCHEMICAL PROCESSES CONTROLLING MINERALIZATION 27

According to a simple principle of thermodynamics, in a 

system consisting of solid, liquid, and gas, if the solid and 

liquid are in equilibrium, also the liquid and gas, then the solid 

and gas must be in equilibrium. It follows directly from this 

that if we have a fluid magma through which gases are rising, 

and if these gases form volatile compounds with the mineral 

matter of the magma or bring it into the gaseous condition in 

any manner, then (provided that there is equilibrium) any 

minerals crystallizing in the liquid portion of the magma will 

have their counterpart in minerals depositing from the gases 

at the contact.

However, the concentration of material in solution 

in the gas or vapor phase may be vanishingly small as 

compared with its concentration in the liquid phase— 

that is, the concentration may suddenly drop on a 

change from a liquid to a gas or vapor phase.

REACTION PRINCIPLE

A mineral relationship that exercises a control over 

the sequence of minerals through a definite order of 

transformation of one mineral into another has been 

described as the reaction principle by Bowen.44 Several 

reaction series as applied to igneous rocks have been 

described, but the mineral changes of the reaction type 

that have the most direct bearing on the replacement 

deposits observed in the Roseland district may be listed 

as follows:

(a) The stability of sodic plagioclase and the instability of calcic plagioclase in the presence of hydrothermal solutions.

(6) The instability of pyroxenes in the presence of a 

certain concentration of water-rich mineralizing solutions and the resulting tendency for their change to 

amphiboles.

(c) The stability of hydrous micas and their tendency 

to form at the expense of feldspar in the presence of 

water-rich solutions.

(d) The tendency for members of the epidote group 

to form from unstable calcic feldspars, pyroxenes, etc., 

in the presence of water-rich solutions.

Certain anhydrous minerals, such as quartz and 

garnet, may also form in the presence of hydro thermal 

solutions.

The ready albitization of calcic plagioclase has long 

been recognized on the basis of geologic observation, 

but Eskola 4S has recently produced this change experimentally under a variety of laboratory conditions. 

He concludes: 46

Anorthite heated under water-vapor pressure with soda and 

silica, either in the form of quartz or of an orthosilicate with 

excessive carbon dioxide from sodium bicarbonate, was changed 

into albite-rich plagioclase. The spilite reaction could thus be 

reproduced.

A general feature of the results is that the reaction and recrystallization was more complete when the temperature was

« Bowen, N. L., The evolution of the igneous rocks, pp. 54-62, Princeton Univ. 

Press, 1928.

u Eskola, Pentti, An experimental illustration of the spilite reaction: Soc. gfiol. 

Finland Comptes Rendus, Extr. no. 9, pp. 1-8. Helsinki, 1935.

«Idem, p. 8.

286089—41——3

below the critical point (of water) than when it was above the 

same point. Thus the experiment at 550° rendered less well 

developed crystals than that at 360°. Best of all vras the 

result at temperatures between 310° and 330°.

Furthermore, it may be noted that only experiments 2, 10, 

and 11, at the lowest temperatures, varying from 264° to 331°, 

gave pure albite, whereas the experiments at 360° or higher 

temperatures, up to 550°, gave oligoclase or even arvdesine. 

This seems to mean that only albite but no anorthite, not even 

as isomorphic mixtures, is stable at temperatures up to 335° or 

a little more.

Bowen 47 makes the following statement about the 

alterations produced by a high concentration of water:

In the presence of a high concentration of hyperfusibles, 

principally water, the ordinary minerals of a gabbro (pyroxene 

and plagioclase) become unstable—that is, liquids of that nature 

are saturated with other phases and will transform pyroxene 

and plagioclase into these other phases to an extent limited by 

the amount of reacting materials available. The instability 

of the plagioclase is characterized by the fact that the one end 

member, albite, remains stable in contact with the liquid, 

whereas the other end member enters into new combinations. 

The result is albitization of some of the plagioclase whicl , theoretically, should be accompanied by at least a little albite newly 

deposited from the liquid. The calcic molecule of the plapoclase 

may in part enter, together with pyroxene material, into the 

constitution of the hydrous phase, amphibole. There will thus 

be a little new-formed amphibole accompanied by transformation 

of some pyroxene into amphibole (uralite). Under other conditions the calcic molecule of the plagioclase forms the hydrous 

zoisite or, acquiring iron from pyroxene, the related epidote, and, 

instead of amphibole, chlorite may appear. The only feature 

of these reactions that has any suggestion of simplicity is the 

great stability of albite. The results of the action of these last 

residual liquors in basic magmas are then albitization, uralitization, saussuritization, chloritization, and epidotization, all 

occurring as late magmatic processes.

This albitization (the formation of NaAlSi3O8 at the 

expense of anorthite (CaAl2Si2O8) is not a eimple 

exchange of bases (that is. an exchange of NarO for 

CaO, for albitization involves an increase in the SiO2 

(or removal of CaO and A12O3) and a substitution of a 

univalent base for a bivalent one. Therefore, when a 

calcic plagioclase is unstable there is an opportunity for 

the formation of other minerals besides albite, those 

formed being the combined result of the new materials 

available in the altering solution and those expelled 

from the unstable mineral.

RELATION BETWEEN ALKALIES AND ALUMINA

The normal order of crystallization in a deep-sQ,ated, 

slowly crystallizing magma is for ferromagnesian 

minerals and calcic plapioclase to precede orthoclase 

and quartz, although a little highly sodic plagio^ase is 

commonly late, and the experiments of Eskola suggest 

that it may belong to the deuteric stage of formation. 

The purely residual portions of magmatic solutions 

commonly contain silica and alkalies, together with 

concentrated hyperfusibles and at times a wide variety 

of rare elements. The widespread geologic evidence of

« Bowen, N. L., Ore deposits of the Western States (Lindgren volumeX p. 114, 

Am. Inst. Min. Met. Eng, 1933.
28 TITANIUM DEPOSITS OP NELSON AND AMHERST COUNTIES, VIRGINIA

alkalic minerals formed in the late deuteric stages of the 

crystallization of an igneous rock, in pegmatites derived 

from it, and in contact-met amorphic deposits where 

sericite may be abundant, shows a strong tendency for 

alkalies to be concentrated into the residual solutions. 

This evidence is so general that we must look for a cause 

in the normal differentiation processes of a crystallizing 

magma. The relation between A12OS and alkalies 

seems to be an important controlling factor in this 

process. The feldspars, feldspathoids, and micas are 

the minerals that commonly fix essential amounts of 

alkalies, as these alkalic aluminous silicates are notably 

insoluble, whereas most of the non-aluminous alkalic 

salts are relatively soluble or unstable.

The magma may not have originally contained 

enough A12O3 to fix quite all the alkalies, as feldspar 

or mica; or the early formation of aluminous pyroxenes 

and amphiboles may leave the last residual material 

deficient in A12O3 . The complete quantitative relation 

between alkalies and A12O3 is not shown by a chemical 

analysis of the final crystallized product of that 

magma—that is, of the igneous rock seen today, after 

the loss of most of the hyperfusible constituents that 

it contained and of the solutes carried with them as 

they escaped. If A12O3 is deficient, the K2O and Na2O 

tend to remain in solution in the residual material of 

most crystallizing magmas. There are, of course, exceptions to this tendency, for in some types of hydrothermal solutions alumina, alkalies, and silica remain 

in solution together. The formation of adularia is one 

example, and another is the formation of alunite 

(K2O.3A12O3 .4SO3 .6H2O) under some conditions. However, these relations indicate that very commonly the 

presence of alkalies in a magma residuum may be 

correlated with the removal of most of the A12O3 

during the normal crystallization of the parent rock, 

so that the escaping solutions carried but little A12O3 . 

This relation probably explains the analytical evidence 

that the secondary minerals in the anorthosite of the 

Roseland district derived their alumina largely from 

the replaced feldspar. Thus the chemistry of differentiation explains the observed results of mineral replacements that did not involve a transfer of A12O3 . 

The alkalies remaining in solution in the magma residuum may have partly escaped with it, provided there 

was no opportunity for them to react with earlier 

minerals of the parent rock. The proportion of alkalies 

thus thrown into the residual solutions need not be 

great to enable them to have an important effect during 

the late deuteric, vein-forming, and contact-metamorphic reactions produced by those solutions.

The concentration of sodium in the residuum of 

many crystallizing magmas is shown by the albitization 

of both potassic and calcic feldspars. This may be 

slight, as where very narrow reaction rims are formed 

around older feldspars or where small amounts of sodic 

micropegmatite or myrmekite are formed at the expense of the feldspars. Oil the other hand, it may be 

very great, as where large masses of rock are albitized.48 

The replacement of microcline by albite las been an 

essential process in the development of a great number 

of pegmatites and shows that essential amounts of 

Na2O are commonly present in the solutions that escape 

from a parent magma into the pegmatite during the 

later stages of pegmatite formation. This replacement 

of potassic by sodic feldspar appears to be most commonly a simple process of base exchange by which 

sodium is abstracted from the replacing solutions and 

potassium restored to them. Several factors, such as 

mass action, greater solubility of albite than of microcline, and instability of microcline, might cause replacement of microcline by albite. However, albitization 

of small amounts of potassic feldspars is not rare in 

rocks where only deuteric processes appear to have been 

active. Where such a replacement occurs in a dominantly potassic rock, an excess of sodium over potassium sufficiently high to cause mass action seems 

improbable. For these reasons a real instability of 

microcline in the presence of hydrothermal solutions 

at moderately low temperatures seems prot able.

The presence of sodium and a deficiency of potassium 

in replacing solutions derived from a rock tl at contains 

potassic feldspar indicate that at some earlier and perhaps pyrogenic stage of crystallization potassic feldspars were stable and had been formed in preference to 

sodic feldspars and thus sodium was concentrated in the 

residuum. The later abstraction of sodium from this 

residuum during the albitization of potassic feldspars 

indicates a reversal of the stability relations of sodic 

and potassic feldspars between the time (pyrogenic?) 

when potassic feldspars were first formed and the time 

(hydrothermal?) of later albitization. Although the 

field evidence for such a reversal of stability between 

potassic and sodic feldspars is widespread, the physicochemical basis for such a change is not understood.49 

Plagioclase may also be partly replaced by muscovite, 

and so potassium may again be abstracted from the 

residual solutions.

PHYSICAL CHARACTER OF REPLACING SOLUTIONS

The effects of the boiling and later condensation of 

the residual portion of a crystallizing magma have been 

described by Bowen 50 as follows:

It has been stated that present in the liquid are H+ , Na+ , 

K+ , Fe+++, and a number of other positive ions, together with 

CP, F~, S , OH~, and all the possible acids, ba^es, and salts 

that these can form. In deciding upon which of these shall 

dominate in the vapor phase let us arbitrarily single out certain 

equilibria for consideration. We have in such solutions an 

equilibrium between KC1, H2O, HCl, and KOH, and all of them 

are to be regarded as present in at least some small proportion.

« Bailey, E. B., and Grabham, W. G., Albitization of basic plaTioclase feldspars; 

Geol. Mag., vol. 6, pp. 250-256,1909. Gilluly, James, Keratophyres of eastern Oregon 

and the spilite problem: Am. Jour. Sci., 5th ser., vol. 29, pp. 225-252, 1935.

« Bowen, N. L., personal communication.

so Bowen, N. L., op. cit. (Lindgren volume), pp. 119,123, 124.
PHYSICOCHEMICAL PROCESSES CONTROLLING MINERALIZATION 29

If a vapor forms in equilibrium with this liquid, which of these 

will enter more freely into the vapor? Certainly not KOH. 

H2O and HC1 will be the principal constituents of the vapor, 

though it will no doubt contain some KC1. Again arbitrarily, 

we may single out the equilibrium between Na2S, NaOH, H2S, 

and H2O. It is plain that in so far as determined by this equilibrium, H2S and H2O will dominate in the vapor. If another 

equilibrium, that between SiO2 , HF, SiF<, and H2O, is considered, 

we note that HF, SiF4, and H2O will enter dominantly into the 

vapor. In the actual complex solution these equilibria are not 

independent of each other, but this fact need not obscure what 

the net result will be. The vapor formed by the boiling of the 

alkaline residual liquors of magmas will be acid, in that it contains an excess of HC1, HF, H2S, CO2 , H3B03 , H2 SO4, and other 

more or less volatile acids. * * *

In an actual example the vapor formed at any point will move 

only a short distance before it encounters a cooler environment, 

where it is partly or wholly condensed, becoming a part of the 

liquid there existing. Though a full and accurate analysis of such 

a complex situation is not possible, it seems necessary to suppose 

that a mass of intrusive rock and its envelope, containing interstitially and in fractures a pegrnatitic liquid that is experiencing 

"second boiling," will constitute itself a fractional-distillation 

column. Throughout this column there occurs a liquid through 

which gas bubbles slowly rise and suffer selective (fractional) condensation. Close to the boiling source the liquid will be continually enriched in the hyperfusible constituents that are relatively nonvolatile; at points more and more remote the liquid 

will become increasingly richer in those hyperfusible constituents 

that are more volatile—water, various halogen compounds including acids, and other substances already suggested as prominent in the vapor phase. * * *

The vapor that boils off from a crystallizing solution, say an 

ordinary salt solution, is in equilibrium with the liquid and with 

the crystals; in other words, it is saturated with the crystals and 

would not attack them in any way so long as it remained a vapor. 

But let the vapor be condensed at lower temperature, and the 

liquid obtained will be wholly out of equilibrium (unsaturated) 

with the same crystals and will therefore attack and dissolve 

them.

Niggli 51 has assigned great importance to mineralization processes occurring above the critical temperature 

and has based a classification of mineral deposits on this 

assumption. However, Morey,52 Fenner,53 and Bowen,54 who are engaged in detailed experimental studies 

of geophysical problems, have all pointed out that 

supercritical conditions need not be assumed, and indeed 

there are valid reasons for doubting the assumption 

that such conditions have exerted a general control of 

geologic processes. Fenner 5S says:

It is possible that at all stages during the cooling of a magma 

the residual liquid holds enough dissolved material so that the 

critical temperature appropriate to it always lies above that 

prevailing at the time. The critical temperature of an aqueoigneous silicate solution is by no means that of pure water but is 

higher by an amount depending upon the quantity of dissolved 

material. Intrusive magmas and the residual liquids derived

81 Niggli, Paul. Ore deposits of magmatic origin—their genesis and natural classification, trans. by H. C. Boydell, London, Thomas Murby & Co., 1929.

62 Morey, O. W., Relation of crystallization of the water content and vapor pressure 

of water in a cooling magma: Jour. Geology, vol. 32, pp. 291-295,1924.

" Fenner, C. N., Pneumatolytic processes in the formation of minerals and ores: 

Ore deposits of the Western States (Lindgren volume), Am. Inst. Min. Met. Eng., p. 

72,1933.

» Bowec, N. L., The broader story of magmatic differentiation briefly told: Idem, 

p. 116.

•' Fenner, C. N., idem, p. 72.

from them doubtless have moderate to very high vapor pressures 

and are able to distill vapors into the pores of enclosing rocks, but 

that does not imply in any way that the supercritical conditions 

postulated by Niggli obtain. The critical temperature of a 

liquid under pressure is that at which it loses its meniscus and 

passes continuously, without change of composition and without absorption of latent heat or discontinuity of any kind, into a 

vaporous form which tends to expand into all the space available 

to it. With respect to the more aqueous residual solutions 

derived from magmas such conditions are theoretically possible, 

but they do not of necessity appear, and it is hardly safe to 

assume their existence without definite evidence.

On the same subject, Bowen 56 says:

Niggli has treated the subject especially in its bearing on the 

formation of mineral deposits. He likewise concluded that under 

deep-seated conditions the external pressure would be adequate 

to prevent boiling, but that, as further concentration of volatile 

constituents goes forward during crystallization, critical phenomena will be exhibited. This is, in its theoretical aspects at least 

a very different matter from boiling, though whethe*- any 

practical criteria can be adduced whereby its results might be 

distinguished from those incident to boiling is not so certain. 

The distinction lies in the fact that when critical phenomena 

occur only one phase is present other than the solid phases. 

This phase is developed from the liquid phase by a process involving no discontinuity in change of properties, though it is in 

many of its properties a gaslike phase. The familiar diffevences 

between gas and liquid no longer exist under critical conditions. 

In the case of boiling, two distinct phases are present in addition 

to the solid phases, and they can be definitely referred to as 

liquid and gas.

The great quantities of material introduced and the 

almost incredible volume of gases or vapors required 

to remove the great quantities of material that have 

disappeared from the replaced rock—all these have 

prevented field observers from accepting some of the 

theoretical conclusions about vapor- or gas-phase 

deposition in several types of ore deposits. In other 

deposits a vapor-phase deposition seems probable. 

Moreover, a vapor-phase may play a dominant role in 

the segregation of mineralizing materials even v^here 

the geologic evidence seems to preclude deposition by 

such a phase.

The mechanism by which a volatile phase mey be 

segregated and its subsequent history are outlined in 

the foregoing quotations from the work of Bowen. 

Under some conditions the greater part of the volatiles 

of the residual material may boil, but probably more 

commonly only a part boils at points where temperatures are highest or pressures are- reduced, and this 

vapor phase rises as a stream of bubbles through a 

column of liquid. In either event the vapor-phase will 

condense where brought into a region of lower temperature. As the acid radicals—F, Cl, SO3 , CO2 , and 

P2O5—are more volatile than bases, they will tend to 

be concentrated in the vapor phase and a liquid phase 

derived from it. The new acid liquid phase formed by 

condensation of the vapor phase, or a phase that had 

remained partly liquid but had become acid by condensation within it of the vapors in a rising stream of

56 Bowen, N. L., op. cit., p. 116.
30 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

bubbles, will be out of equilibrium with the crystal 

phase of the parent rock and will tend to dissolve its 

bases or the bases of any rock traversed so long as the 

acid character persists. The least stable minerals in 

contact with it will be first attacked, and in general 

these are ferromagnesian and calcic silicates, such as 

olivines, pyroxenes, and calcic plagioclase.

SOURCE OF FEKROMAGNESIAN MATERIALS

The normal crystallization sequence in deep-seated 

igneous rocks is ferromagnesian minerals and calcsoda feldspars followed by alkalic feldspars and quartz; 

and this tends toward the early depletion of the residual 

magma in ferromagnesian materials and calcium. 

Nevertheless, there is widespread geologic evidence for 

the introduction of great quantities of ferromagnesian 

and calcic materials during hydrothermal stages of 

mineralization in a wide variety of mineral deposits. 

The writer 57 has given reasons for believing that ferromagnesian constituents, although originally in large 

part abstracted during an early magma stage of crystallization, may subsequently be restored to the residual 

solutions of the same magma by a deuteric process of 

base exchange or mineral replacement.

A large proportion of all igneous rocks show evidence 

of deuteric reactions that would tend to release bases 

to the residual solutions. Certain ferromagnesian 

minerals are unstable in the presence of an excess of hot 

hyperfusibles, and the change from a nearly anhydrous 

to a water-rich environment—commonly the concentration of H2O in the residuum through crystallization 

of anhydrous minerals—tends to cause the alteration 

of olivine to serpentine and of pyroxenes to amphiboles. 

The albitization of calcic plagioclase or its replacement 

by muscovite in the presence of residual solutions 

carrying alkalies will release calcium, which in turn 

tends to react with orthorhombic pyroxenes to form 

amphiboles and release MgO and FeO according to the 

following equation:

8[(Mg,Fe)O.Si02]+2CaO+H2O^[H2O.2CaO.5(Mg,Fe) 

O.8SiO2] +3 (MgO.FeO).

On the other hand, the alteration of diopsidic pyroxene 

would tend to fix MgO, and release CaO. However, 

orthorhombic pyroxenes are much less stable than 

diopside. If calcic feldspars are abundant and are 

undergoing alteration, these reactions may give a 

dominance of CaO in the residual solutions, but if there 

is a large proportion of orthorhombic pyroxene undergoing alteration the CaO may be largely used up in 

deuteric reactions within the parent rock, so that little 

escapes, and MgO and FeO become dominant in the 

escaping solutions.

CHEMISTRY OF REPLACEMENT

Igneous rocks are commonly composed of diverse 

groups of minerals with widely differing and but p'oorly

understood stabilities. These minerals may be altered 

or replaced under the influence of solutions whose composition is in general inadequately known. T^hen such 

a rock is subjected to alteration, the relations are so 

complex that the chemistry of the processes c^n be only 

approximated. In contrast, the Roseland anorthosite 

was originally an almost pure feldspar rock that contained only SiO2 , A12O3 , CaO, K2O, and Na2O in essential amounts. This rock was altered by solutions that 

introduced TiO2 , Fe2O3 , FeO, MgO, and P2O5 in essential amounts, and small quantities of F, Cl, CO2 , and 

rarer materials. These relations present ar opportunity for determining the chemistry of the replacement 

of feldspars and the development of secondary silicates. 

It does not present an equal opportunity for determining the chemistry of the replacement by rutile, ilmenite, 

and clinohypersthene, as they appear to have been 

formed by the complete removal of feldspar and the 

deposition of entirely new materials in their stead. The 

record of the steps in the replacement have thus been 

obscured and there is, therefore, little that forms a basis 

for determining the chemistry of the process.

The formation of clinohypersthene was a local episode 

that was followed by one during which the ent:re anorthosite mass anJ the contact rocks were mineralized. 

This is represented by the formation of apatite, rutile, 

ilmenite, quartz, amphiboles, micas, and cHnozoisite 

and presents an unusual opportunity for the study of 

replacement processes. This replacement was effected 

by mineralizing solutions and is believed to have been 

a nearly continuous process, although there was no 

doubt a sequence in mineral formation, whi".h reflects 

changes in the composition and physical character of 

the solutions.

The disseminated deposits show zonal re7 ations, as 

ferrous iron minerals (ilmenite, actinolite, and biotite) 

are limited to close proximity to feeding channels, and 

outside of this is a zone in which low-iron tremolite 

recording the introduction of MgO was formed in association with rutile, sericitic muscovite, and e'inozoisite. 

In the outermost zones clinozoisite and sericitic muscovite were formed without the introduction of new materials other than H2O and a little F and CO2 . These 

zonal relations indicate that the bases represented in 

the secondary minerals tended to drop out of the incoming solutions, although with much overlapping, in the 

order FeO, TiO2, MgO, CaO, K2O, and Na3O. Fe2O3 

was also added, but its place in the order of deposition 

is not clear, although the formation of magnetite veinlets in ilmenite indicates that the degree of oxidation of 

iron was greater in the later stages. The relations indicate that the CaO and Na2O were derived almost 

wholly from andesine undergoing alteratior, and the 

K2O was probably hi part derived from microcline.

The zonal distribution of the secondary minerals is 

not sharply limited, for the continued flow o^ solutions

Ross, C. S., Origin of the copper deposits of the Ducktown type in the southern AppaJacMan region: U. B. Qeol. Survey Prof. Paper 179, pp. 52-54,1935.
PHYSICOCHBMICAL PROCESSES CONTROLLING MINERALIZATION 31

caused one mineral zone to overlap another, but they 

contribute to an understanding of the physical chemistry of replacement processes. In the following discussion, the mineralogic and chemical changes are 

considered in the order indicated by these zonal relations.

Some of these minerals (the micas, for instance) do 

not have a fixed chemical composition, but the following 

representative formulas may be used, as variations from 

them would only change the proportions slightly but 

not the essential relations. For simplicity of calculation the formulas are expressed in the form of oxides.

Mineral formulas

Anorthite = 2Ca0.2Al2 03 .4Si02 or Ca2Al2 (Al2Si4)Oi 6.

Albite = Na2O.Al2 03 .6Si02 or Na2Al2 (Si2Si4) 016 - Microcline = K2O.Al2 03.6Si02 .

Biotite =H2O.K2 0.4(MgO, FeO).2Al2 03.6Si02 .

Muscovite = 2H2O.K2 0.3Al2 03.6Si02.

Clinozoisite=H2 0.4Ca0.3Al2 03.6Si02.

Tremolite = H2 0.2Ca0.5Mg0.8Si02 .

Actinolite = H2 0.2Ca0.5(Mg, Fe)0.8Si02.

It should be noted that the formula for anorthite as 

commonly written (CaO.Al 2O3 .2SiO2) corresponds to 

only one-half of the formulas for albite and microcline, 

and therefore the anorthite formula has been doubled.

The feldspar undergoing alteration was andesine, an 

isomorphous mixture of approximately 1 part of anorthite to 2 parts of albite, associated with about a part 

of antiperthitic microcline—that is, about Ab2An1Orl .

Water, being the most abundant solvent, was also 

present in excess, but as this solvent water occurs on 

both sides of the equations, it can be neglected, and 

only the water that enters directly into the chemical 

reactions need be included. Other hyperfusibles that 

may have accelerated but did not take part in the 

reactions have also been neglected. Andesine expressed

as 2 parts of albite plus 1 part of anorthite appear? on 

the left side of the equations, and the new albite 

released by reaction appears on the right. In the same 

way microcline may appear on both sides of the eouations. These are not canceled, because the prinary 

feldspar had a fixed composition, and it seems advisable 

to include the complete feldspar composition of the 

reacting materials rather than only the unstable and 

reacting part of the feldspar. To do so would obscure 

the mineralogic relations, which are as essential as the 

chemical relations for presenting a clear picture of the 

reactions involved. The alteration of plagioclase is not

but is

andesine

anorthite-^clinozoisite, etc. 

2 albite 1

1 anorthitej ^albite -fclinozoisite, etc.

That is, albite is just as much a secondary product of 

reaction as clinozoisite and the related minerals.

In the following equations the mineral formulas— 

both before and afte» the reaction—represent observed 

minerals whose chemical composition is closely known, 

whereas the amounts of the solutes added or abstracted 

during the reaction are deduced through a balancing of 

the equations. In order to present the transformation 

as clearly as possible, the names of the minerals involved 

are given directly below their chemical formulas.

The reactions near the zone where FeO and MgO 

were available in the solutions and biotite and actinc Jite 

were formed can be represented by the following 

equation:

Equation 1 represents the inner zone of most intense alteration. The new elements introduced form 

only about 10 percent of the resulting rock, although 

there has been a very thorough change in the mineral 

composition.

riO[Na2O.Al2 03 .6Si02 n

L5[2Ca0.2Al2 03 .4Si02]J

Andesine

5[K2O.Al203 .6Si02] Microcline

21[FeO, MgO]+7H2 0

Solutes

Equation 1

10[Na2O.Al2 03 .6Si02] 

Albite

+

2[H2 0.4Ca0.3Al203 .6Si02] 

Clinozoisite

+

[K2O.Al203 .6Si02] Microline

4[H2O.K20.2Al2 03 .4(FeO, MgO).6Si02] 

Biotite

Ilmenite also was formed in this zone, but it should 

be noted that equation 1 does not express the reactions 

resulting from its introduction.

Equation 2 represents the intermediate zone where

[H2 0.2Ca0.5(FeO, MgO).8Si02 ] 

Actinolite

about 2.5 percent of new material has been added and 

a slightly smaller proportion of new minerals developed 

than in the zone represented by equation 1.
32 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

Equation 3

riO[Na2 O.Al2O3 .6SiO2 ]-|

|_5[2CaO.2Al2O3 .4SiO2 ]J

Andesine

+

5[K2O.Al2 03 .6Si02 ] 

microcline

+

5MgO + 5H2 O 

solutes

This is the zone characterized by rutile, but, as in 

equation 1, the introduction of TiO2 is not represented.

The microcline has tended to resist alteration, while 

K2O has been introduced, at least locally. The formation of sericitic muscovite at the expense of andesine

10[Na2O.Al2 O3 .6SiO2] 

albite

2[H2O.4CaO.3Al2 O3 .6SiO2 ] 

clinozoisite

3[K2O.Al2 O3 .6SiO2 ] 

microcline

2[H2O.K2 0.3Al2 03 .GSi02] 

muscovite

[H2O.2CaO.5MgO.8SiO2 ] 

tremolite

would tend to release Na2O in the zones of most intense 

replacement. This tendency is illustrated by another 

slight modification of equation 2 and is shown in 

equation 3.

Equation 3

riO{Na2O.Al2O3 .6SiU2 n

L5[2CaO.2Al2O3 .4SiO2 ]J

andesine

5[K2O.Al2O3 .6SiO2 ] 

microcline

5MgO + 5H2 0

solutes

8[Na2O.A] 2 O3 .6SiO2 ] 

albite

The Na2O released by the replacement shown in 

equation 3 migrated but a short distance before reacting 

with andesine to produce albite (albitization). This 

process also involved the introduction of some SiO2 ,

2[H2O.4CaO.3Al2 O3 .6SiO2 ] 

clinozoisite

+

5[K2O.Al2 O3 .6SiO2 ] 

microliiie

+

2[H2O.K2O.3Al2 O3 .6SiO2 ] 

muscovite

+

LH2O.2CaO.5MgO.8SiO2 ] 

tremolite

+ 

NaoO

and the CaO released from the replaced feldspar 

(anorthite molecule) formed clinozoisite. TMs type of 

replacement is shown in equation 4.

Equation 4

f 4[Na2 O.Al2O3 .6SiO2 ] ~\\

L2[2CaO.2Al2O3 .4SiO2 ]J

Andesine

+

2[K2O.Al2 O3 .6SiO2] 

Microcline

Solutes

Equation 5 represents relations throughout the 

anorthosite. Here only a little water was introduced, 

and a marked change in mineral composition was 

caused merely by a rearrangement of the materials of -

5[NaoO.Al2O3 .6SiO,] 

Albite

[H2 0.4Ca0.3Al2 03 .6Si02] 

Clinozoisite -

+

2[K2O.Al2 O3 .6SiO2 ] 

Microcline

the primary rock. Albite and the elements that 

recrystallized into clinozoisite were released from the 

andesine, and some of the microcline formed muscovite.

Equation 5

f 8[Na2O.Al2 03 .6Si02 ] 

L4[2CaO.2Al2 p3 .4SiO2 ] 

Andesine

+

4[K2O.Al2O3 .6SiO2 ] 

Microcline

+

3H2O 

Water

8[Na2O.AloO3 .6SiO2 ] 

Albite

+

[H2O.4CaO.3Al2O3 .6SiO2] 

Clinozoisite

+

3[K2O.Al2 O3 .6SiO2 ] 

Microcline

+

[H2O.K2O.3Al2 O3 .6SiO2 ] 

Muscovite

+

4SiO2 

quartz
PHYSICOCHEMICAL PROCESSES CONTROLLING MINERALIZATION 33

These equations, for the sake of simplicity, have 

assumed complete alteration of the unstable anorthite 

molecule to new minerals. Actually only part of this 

molecule was altered, and varying proportions of it, 

together with corresponding amounts of albite and 

microcline, should appear on both sides of the equations. Thus plagioclase represented by various proportions of anorthite and of albite molecules should appear 

on the right-hand side of the equation and would vary 

from albite (Ab93Ab7) in zones of most intense alteration to andesine (Ab67An33) where alteration was slight.

These long equations could have been represented by 

several shorter ones. For instance, the alteration of 

anorthite to clinozoisite could be represented as a single 

reaction releasing A12O3 and SiO2 . Then microcline 

could be represented as partly altering to muscovite 

and at the same time combining with the released 

A12O3 . However, it is believed that the method of representation used gives a clearer picture of the changes, 

and the fact of the transfer of elements from one mineral to another will be understood. Clinozoisite, 

muscovite, and tremolite commonly formed evenly 

disseminated microscopic grains within the altered 

feldspar. Thus most of the movement was so local 

that diffusion within the solid cyrstals was adequate for 

the transfer. The most static radical was evidently 

A12O3, and probably Na2O was the most mobile and 

migrated farther from its place of release than any of 

the other materials. Some CaO and no doubt some 

K2O, however, escaped into the surrounding rocks to 

form calcite and sericite.

The preceding equations doubtless do not present a 

perfect picture of the chemical processes that took place 

in the anorthosite; but it seems evident that modifications would not change the essential relations but 

change only slightly the proportions. The volume 

relations are not shown by the equations. However, 

such new minerals as micas, amphiboles, and clinozoisite have a greater density than the feldspar replaced 

and would tend to compensate the volume relations 

resulting from the introduction of materials. The use 

of specific gravities of the minerals given in standard 

textbooks makes it possible to calculate closely the 

relative volumes of the old and new minerals. Such 

calculations indicate that the mineral transformations 

represented in equation 1, where about 10 percent of 

new material was added, would result in an increase in 

volume of only about 2 percent. All the other equations would represent a loss of volume. As alteration 

was rarely as complete as represented in equation 1, 

the general effect would be a loss rather than a gain in 

volume.

Notwithstanding obvious qualifications, the equations agree so completely with the actual mineral transformations that they seem to give au essentially correct 

picture of the chemical changes that controlled replacement in the Roseland anorthosite. The equations also

indicate the chemical reason for the formation of two 

or more minerals—usually a mica and an amphibole or 

clinozoisite—during a single stage of alteration of the 

andesine. The materials released by the replacement 

process could not recrystallize into a single new mineral, 

and two or three new ones were formed.

The equations serve to show that the introduction 

of 110 new material except H2O and a very little F need 

be assumed in explaining alterations in the outermost 

zone of mineralization in the anorthosite. For this 

reason it seemed advisable to have an analysis mr.de of 

the highly altered rock, to compare with an analysis 

of the primary feldspar which had previously been 

made. A specimen containing a very large proportion 

of muscovite and clinozoisite was obtained from the 

quarry of Dominion Minerals, Inc., on the Piney Fiver, 

and the analyses of this and the primary feldspr.r are 

given below.

Chemical analyses of fresh and altered feldspar 

[J. Q. Fairchild, analyst]

SiO2 --- ----------------------------

A12O3 --- ------------------ ----------

FeFeO 2O3 \ fa& F *eu__ Q — _----_--- — __--- — - 

MgO_--------- .----_---_--_-_--._

CaO---- --------------------------

Na2O__-- --------------- ------------ K..O

BaO_ — _ __--_- ---------------

H2O--- ------------------- --------

H2 0 + — — — - — ----------------

TiOo— _ — __-----_--- — — --__

Fresh

61. 44

23. 47

. 20

. 05

5.00

5.94

3.92

. 19

.03

. 20

. 10

100. 54

Altered

59. 62

24.06

f .49

X .09 

.07

4.54

5. 47

4.53

. 03

1. 19

OQ

100. 18

The two analyses are surprisingly similar when it 

is remembered that the second one represents a very 

great change in mineral composition. There has been 

a small loss of CaO and Na2O and a gain hi K2O. This 

change is to be expected from the tendency for K2O to 

become fixed at the expense of Na2O, as discussed on 

page 27 and represented in equation 3. The limited 

ability of FeO and MgO to travel far from feeding 

channels is also shown by the analyses. Ferric iron 

has been slightly increased in the altered rock and 

proxies A12O3 in clinozoisite.

SOURCE AND CHARACTER OF THE SOLUTIONS

The processes going on at the source of mineralizing 

solutions can never be observed directly. However, 

evidence about the early history of escaping solutions 

may be gained from their effects on the invaded rocks, 

as interpreted in the light of chemical and geophysical 

experiment.

The parent magma supplying introduced materials 

undoubtedly underwent progressive crystallization in 

depth and tended to concentrate hyperfusibles in its 

residuum. When these reached a certain concentration
34 TITANIUM DEPOSITS OF NELSON AND AMHEEST COUNTIES, VIRGINIA

and pressure they tended to escape, carrying with them 

certain soluble materials. The minerals deposited indicate that the escaping solution carried the bases 

FeO, TiO2 , MgO, Fe2O3 , some K2O and SiO2 , but 

probably only minor amounts of other bases.

The greatest concentration of any hyperfusible other 

than water is the P2O5 of apatite. However, apatite 

contains essential amounts of fluorine (2.5 percent) and 

a little chlorine. The more widely distributed sericitic 

muscovite and even the clinozoisite (see p. 12) contain 

small amounts of F, and the total amount in the Roseland rocks probably exceeds the more localized 

amount in apatite. The dominance of fluorine over 

chlorine is shown by the composition of the apatite. 

(See p. 14.) No barite was formed, although the 

presence of barium is shown by the feldspar analysis. 

(See p. 10.) Therefore, SO3 was probably not 

present in essential amounts in the solutions, although 

the sparse but widely distributed pyrite and pyrrhotite 

show that sulfur was present in some form during a late 

stage of mineralization. The occurrence of calcite 

shows the presence of CO2 in the mineralizing solutions, 

and graphite indicates that carbon was locally introduced in some unknown form. Thus the hyperfusibles 

that may have played a part in the segregation and 

transfer of mineralizing materials appear to be H2O, 

P2O5, F, and a little Cl and CO2 .

MODE OF SEGREGATION AND TRANSPORTATION OF 

MINERALIZING MATERIALS

PHOSPHORUS

Apatite, with about 40 percent of P2O5, is abundantly 

present in the nelsonite bodies and locally in the disseminated deposits and appears to have been one of the 

earliest minerals to be formed during the mineralization 

of the anorthosite. It was preceded only by the pyroxene and some of the quartz. Therefore, phosphorus 

seems to have been selectively segregated from the 

parent magma during the earlier, hotter stages of the 

evolution of mineralizers.

Apatite is one of the earliest minerals to be formed 

during the magmatic stage of the crystallization of 

igneous rocks and is stable at very high temperatures. 

Thus the formation of apatite tends to remove P2O5 

from the magma at an early stage of crystallization, 

at a time when the concentration of P2O5 is very low.

The chemical composition of a wide variety of igneous 

rocks shows that P2O5 is almost always present as one 

of the acid radicals, and yet phosphate minerals are 

commonly sparse in mineral deposits formed by magmatic solutions. Therefore, P2O5 is probably not 

normally a member of the group of materials that tend 

to be concentrated in a hyperfusible rich magma 

residuum. This indicates that in the rare type of deposits where apatite is abundant, some mechanism of 

segregation different from that occurring in most

mineral deposits was active. Perhaps a later reaction 

with early products of crystallization reT eased P2O5 

and restored it to the residual solutions after water and 

other hyperfusibles had reached a high derrree of concentration.

An acid vapor phase seems the mort probable 

mechanism for the removal of phosphorus from the 

parent rock, as the apatite of the nelsonite bodies was 

introduced by solutions in some form. A vapor phase 

composed dominantly of H2O enriched in acid radicals, 

asdescribed on pages 28, 29, would probably tend to keep 

P2O5 in solution or to break down apatite and release 

P2O5 . Very little is definitely known about the behavior 

of phosphorous compounds at high temperatures and 

pressures, but phosphorous acid is moderately volatile. 

Many of the compounds of P2O5 studied at low temperatures are reported to break down in the presence of 

water, or at only moderately high temperatures. However, the very high pressures that must have existed at 

the profound depths at which P2O5 was segregated 

would, in general, increase the range of stability, so that 

most compounds would remain stable at temperatures 

higher than those ordinarily studied. Several combinations of phosphorus with the other materials of a 

vapor phase are possible. However, no information 

on phosphorous compounds is available thr,t permits a 

definite prediction of the compounds that would 

dominate a vapor phase under high pressures, and it is 

therefore not possible to state any definite boiling point. 

Even though this were moderately high, the partial 

pressure effect would permit an excess of vater vapor 

to carry over essential amounts of phosphorous compounds, provided they were stable in its presence. 

This would probably imply distillation of a T~apor phase 

of P2O5 at higher temperatures and probably its escape 

at an earlier stage of crystallization than that characterizing most mineral deposits.

A liquid-phase extraction of P^Os seems improbable 

for the following reasons. A residual solution that has 

remained in a liquid phase throughout its history has 

been in contact with easily alterable ferromagnesian 

and alkalic minerals and so must have remained essentially neutral. Apatite seems to be stable in such a 

medium, and any P2O5 tending to remain in solution 

would be in an environment rich in calcium and iron 

minerals and could immediately react with them to 

form very insoluble compounds of these elements.

The sharp restriction of apatite to nelscnite bodies 

or to small veinlike areas in the anorthosite, while other 

calcium minerals were formed outside of these areas, 

suggests that the development of apatite was more 

dependent on supplies of P2O5 than of CaO. This tends 

to confirm the evidence, which is more conclusively 

presented by the silicate minerals and analyses of fresh 

and altered rock, that local supplies were the main 

source of CaO. However, some of the CaO of the 

nelsonite highest in apatite was probably introduced
PHYSICOCHEMICAL PROCESSES CONTROLLING MINERALIZATION 35

or locally concentrated from other parts of the anorthosite undergoing alteration.

TITANIUM

The chemistry of the segregation of titanium presents 

a complex problem, but an essential one in the paragenesis of the titanium deposits. As pointed out on 

page 34, the hyperfusibles that need to be considered 

as possible mediums of transfer are H2O, P2OS , F, and 

a little Cl and CO2 .

First we may examine the probable reactions of 

titanium with these acid radicals in a liquid phase. 

Titanium phosphate is very insoluble in neutral solutions, and so TiO2 and P2O5 were probably not introduced together, and this is confirmed by the mineralogic 

evidence that apatite was earlier than rutile and ilmenite. No titanium carbonates are known, and potassium 

titanic carbonate, though soluble, probably is not 

stable at high temperatures in the presence of water, 

so that CO2 probably played no part in producing a 

soluble form of titanium. The alkali titanites are 

probably not stable, for although they are soluble, 

they are broken down into insoluble hydroxides on 

boiling.

Ilmenite is promptly precipitated in the presence of 

ferrous iron minerals, as shown by the restricted zone 

of ilmenite in the Roseland area. It is also shown in 

the diabase at Goose Creek described by Shannon.68 

Here a normal diabase and a diabase pegmatite are 

characterized by titanium-bearing pyroxene. In parts 

of the diabase pegmatite this pyroxene has been 

altered to a paler variety and the titanium released to 

the solutions, which migrated out into the normal 

diabase. Here it came into contact with disseminated 

magnetite and was precipitated as aggregates of 

hematite and ilmenite, so that it was removed from 

solution before it had moved more than 20 or 30 centimeters from its source. Therefore it seems probable 

that if titanium in some soluble form entered a liquid 

phase while in direct contact with the varied minerals 

of a ferromagnesian rock, there would be a ready 

opportunity for it to combine with FeO to produce 

insoluble titanium minerals. This is what happened 

when titanium-bearing solutions entered the ironbearing rocks now exposed, and the same reactions may 

be supposed to have occurred in deeper-seated rocks. 

That is, geologic evidence indicates that titanium is 

precipitated in the presence of ferrous iron under a 

wide range of physical conditions, and it seems improbable that titanium was segregated, transported, and 

deposited in the presence of FeO by a solution that 

remained in a liquid phase throughout its history.

A vapor phase of titanium seems capable of explaining a segregation of titanium from rocks with a normal

ss Shannon, E. V., The mineralogy and petrology of intrusive Triassic diabase at 

Goose Creek, Loudon County, Va.: U. S. Nat. Mus. Proc., vol. 66, art. 2, no. 2539, 

pp. 1-86, 1924.

286089—41———4

iron content. Titanium characterizes many ferromagnesian igneous rocks and may be present as disseminated 

ilmenite, as sphene, or as titaniferous pyroxenes. 

However, no primary, undoubtedly pyrogenic rocks 

appear to be known in which iron is not in large excess' 

over titanium. Therefore it seems difficult to picture 

a truly pyrogenic process of magmatic differentiation 

that would result in the excess of titanium over iron. 

On the other hand, a fluorine-rich vapor phase that 

distilled titanium over together with but little ferrous 

iron seems to be a logical mechanism for bringing g,bout 

a high concentration of titanium from a parent rock 

in which iron and titanium were present in ncrmal 

proportions.

The solutions that introduced titanium minerals into 

the sedimentary rocks of the Magnet Cove region of 

Arkansas were emanations from igneous rocks of the 

immediate vicinity, or from more deep-seated rocks 

similar to those exposed at the surface.

The following analyses 59 represent two typical Magnet Cove rocks:

Analyses of Magnet Cove rocks 

[H. S. Washington, analyst]

SiO2 __-_- ________________ ___________

A12O3 --- ----------------------------

Fe2O3- __-_-__-__-_-----_------_--_-

FpO

MgO — .- — _ — — — ———— — —

CaO— .-_- ——— — —— — —— ——

Na2O--_ ---------------------------

KSO_——— _--_ — — _--- — —— ——

H2O--_--_---_-------- -------------

H.O + — —— —— -- ——— _ —— - ———

Ti02 _ ------------------------------

ZrO2 _ __ — ___ — ___ — _____ — — _ — — „

CO2 __ _-___--___ „_ ——— ______„ __„

P2 05 _ — ---------------------------

Cl_ ____--_- ___------_-----_----_-

S -- --- ._ -

MnO----_ --------------------------

BaO ___----__---------_--------- -

i

41. 75

17.04

6. 35

3.41

4. 71

14.57

6. 17

. S. 98

.28

.62

.58

.05

None

1.09

None

Trace

None

100. 60

2

53.09

21. 16

1.89

2.04

.32

3.30

6.86

8.42

.24

1. 13

. 11

.04

.82

. 15

.02

.08

.20

. 61

100. 48

Locally, rocks higher in TiO2 are present hi the 

Magnet Cove region, but many of these show evidence 

of post-magmatic alteration, and have clearly been 

enriched in titanium. Another rock from Mp,gnet 

Cove analyzed by Washington 60 had probably been 

enriched in titanium and contained TiO2 4.54 percent, 

total iron 15.24 percent, and FeO 6.17 percent.

The analyses show the preponderance of total iron 

and also of ferrous iron over titanium. In one the total 

iron is nearly 17 tunes as abundant as titanium and 

in the other 36 tunes. In a third analysis (not shown 

in the table), which had probably been enriched in

» Washington, H. S., Igneous complex of Magnet Cove, Ark.: Geol. Soc. America 

Bull., vol. 21, p. 399, 1900; The foyaite-ijolite series, Magnet Cove, Ark., a chemical 

study of differentiation, Jour. Geology, vol. 9, p. 611,1901.

w Washington, H. S., Jour. Geology, vol. 9, p. 620,1901.
36 TITANIUM DEPOSITS OF NELSON AND AMHERST COUNTIES, VIRGINIA

titanium, this element was 5 times as abundant as 

iron. Notwithstanding this excess of iron, the hyperfusibles escaping from these rocks, deposited abundant 

titanium minerals. Locally, titanium minerals were 

'formed almost to the exclusion of iron minerals— 

that is, physico-chemical forces were at work that resulted in a selective concentration of titanium from a 

rock in which iron was many times as abundant as 

titanium.

Titanium tetrachloride is relatively volatile, with a 

boiling point of 136° C. at atmospheric pressure, but 

is so readily hydrolyzed in the presence of water that 

its volatilization in the laboratory is possible only under 

carefully controlled anhydrous conditions. Titanium 

tetrafluoride has a higher boiling point than the tetrachloride, 285° at atmospheric pressure. It also tends 

to hydrolyze under normal temperatures and pressures 

but less strongly than the tetrachloride.

The tendency for the tetrafluoride to hydrolyze 

raises a question as to the possibility of the formation of 

a vapor phase in the presence of water. However, it 

seems probable that hydrolysis would tend to be inhibited under the very high pressures and the accompanying high temperature that must have existed in 

the very deep-seated pre-Cambrian parent rock. The 

titanium deposits may well have formed at a depth of 

several miles, and the parent magma of the mineralizing 

solution must have lain still deeper. The boiling point 

of titanium tetrafluoride under these deep-seated conditions would probably be raised to about the figure 

that is to be inferred at the time an early vapor phase 

was escaping from a crystallizing magma.

Another factor that would tend to inhibit hydrolysis 

of titanium at high temperatures has been pointed out 

by Burbank.61 Any vapor phase must have been in 

intimate contact with ferromagnesian, aluminous, and 

alkalic minerals of the parent rock and the rocks traversed during its escape. These minerals and especially 

feldspars, pyroxenes, and olivine would themselves 

have a strong tendency to hydrolyze and so remove 

water from the system, especially as their abundance 

would exert a strong mass-action effect. The hydrous 

minerals micas and amphiboles form and are able 

to remove water from the system in even typically 

pyrogenic rocks, where the water concentration must be 

very low. In the Roseland district micas, amphiboles, 

and clinozoisite have formed throughout the anorthosite, 

in the ferromagnesian dikes, and probably also in the 

parent rock of which they are apophyses. This must 

have resulted in a large removal of water from the 

mineralizing medium. There is, then, evidence that 

seems to make it probable that titanium was segregated 

as a vapor phase of titanium tetrafluoride, which was 

distilled over from the residual solution of a partly 

crystallized parental magma.

61 Burbank, W. S., personal communication.

Were adequate amounts of F present to I ring about 

such a transfer? The F in the apatite certainly does 

not represent any such amounts, but the minute percentages in sericitic micas and clinozoisite, which are 

present throughout the anorthosite mass, must be 

large in the aggregate, and the quantity of F that 

undoubtedly escaped into contiguous rocks was doubtless larger still. The amount of F, therefore, was 

evidently far in excess of that required to transport all 

the titanium, which after all is local in its occurrence.

The titanium deposits at Magnet Cove, Ark., present 

mineral relations that seem not inconsistent with such 

an origin. Here titanium has been carried far into a 

pure quartz sedimentary rock, and taeniolite, a mineral 

carrying 13 percent of F, has formed abundantly. 

The same medium that introduced titanium removed a 

large proportion of the silica and recrysl allized the 

remainder into comparatively large euliedral quartz 

crystals. A vapor phase rich in fluorine S3ems a not 

improbable explanation of these relations.

As the magma cooled the temperature must have 

fallen below the boiling point of one after another of 

the constituents of a vapor phase. As the boiling point 

of titanium tetrafluoride was evidently rather high, that 

constituent may have practically disappeared from the 

system at an early stage. Of course, if any material of 

higher volatility continued to boil off, it vould carry 

with it a certain amount of material of lowe^ volatility, 

owing to the partial pressure effect. There would not 

be an entirely sharp elimination of any volatile constituent as the temperature dropped below its boiling 

point, although there probably would be a very sudden 

drop in its concentration. If a liquid phase became 

dominant titanium probably almost ertirely disappeared from the escaping solutions.

IRON, MAGNESIUM, AND CAJLCIUM

The chemical conditions that would permit the 

segregation of iron are intimately connected with its 

relation to titanium and to magnesium and calcium. 

The acid radicals that should be considered are the 

same as those for titanium—that is, H2O, PgOs, F, Cl, 

and CO2.

Ferrous iron salts of all these radicals have very low 

vapor pressures, and those of magnesium f,nd calcium 

are even lower. This would not inhibit their presence 

in a vapor phase, but their segregation in essential 

amounts in the vapor phase seems improbable. On 

the other hand, the transportation of ferrous iron bicarbonates or halogens in a liquid phase is quite possible. 

The conditions for the volatilization of ferric halogens 

are more favorable, as ferric chloride vaporizes at 280° 

and the fluoride at about 1,000°, atmospheric pressure. 

However, chlorine seems not to have beer abundant, 

and the vapor pressure of the fluoride is rather high. 

Therefore, the concentration of ferric iron in a vapor
PHYSICOCHEMICAL PROCESSES CONTROLLING MINERALIZATION 37

phase was probably low, although it was probably 

present, and it may have been augmented by the 

partial pressure effect. Thus a large volume of gas may 

have been the segregating if not the transporting agent 

for the ferric iron that forms a small part of the widely 

disseminated clinozoisite. However, a liquid phase as 

a source seems possible, especially as magnetite, with 

its higher Fe2O3 content was formed in a later and 

probably cooler stage than ilmenite, in which the iron is 

in the ferrous state. The geologic relations also show 

that FeO and MgO were introduced together, but 

probably not by a liquid-phase solution that also contained P2O5 or TiO2 .

Some calcite is present in the border facies of the 

anorthosite, in the adjacent country rock, and in the 

pegmatitelike zones. The CaO of this calcite may have 

been introduced together with the MgO and FeO of the 

ferromagnesian silicates, as the greater solubility of 

CaCO3 would favor its migration to greater distances 

from the feeding channels, where the lower temperatures 

might permit the formation of a carbonate. However, 

the analyses given on page 33 show that the solutions tended to remove rather than introduce CaO, 

and it seems probable that the CaO in these outer zones 

was released from the altered andesine.

The approximate absence of CaO in solutions that 

were introducing FeO and MgO may be due to the 

stability or the sparsity of calcium minerals in the parent 

rock. A much more probable explanation, however, is 

the removal of CaO from the solutions before or during 

their escape, as a result of the extensive alteration of the 

hypersthene type of pyroxenes to amphiboles described 

on page 30.

RESTATEMENT OF PARAGENESIS

The foregoing considerations indicate that the most 

probable sequence and mode of segregation of the 

mineralizing materials of the Roseland anorthosite was 

as follows: The P2O5 of the apatite, together with 

smaller proportions" of F and a very little Cl, was concentrated as a vapor phase that distilled over at high 

temperature and pressure. This may have reached 

the point of deposition as a vapor phase or condensed 

and completed its journey as an acid liquid phase. The 

calcium of apatite was probably derived either locally 

or with slight transportation from the calcium feldspar 

of the replaced anorthosite. Slightly later, titanium 

also was distilled over as a vapor phase of titanium 

tetrafluoricle at comparatively high temperature and 

pressure. As cooling progressed, a liquid phase became 

dominant, and ferrous iron and magnesium materials 

characterized by very low vapor pressures but moderate 

solubilities in a liquid phase were segregated from the

parent rock. The earliest of the ferrous iron, which 

reacted with rutile to form ilmenite and formed ferromagnesian silicates, may have been carried in soT ution 

in part as a halogen salt, but, at least during the later 

stages of mineralization, ferrous iron and magnesium 

may have been transported as bicarbonates.

Calcium is normally concentrated slightly before 

magnesium and ferrous iron, as it is the most soluble 

of the three carbonates. The conditions within the 

source rock, however, were such that very little calcium 

escaped, and that released through the alteration of 

plagioclase was probably fixed within the parent rock 

by the alteration of pyroxenes to amphiboles. Small 

amounts of CaO were probably derived from the 

anorthosite, rather than from the parent ferromagnesian 

rock, and locally concentrated. Silica was not sharply 

limited to a single stage of mineralization, and most of 

it was probably derived from the alteration of the 

anorthosite itself. The period of introduction of ferric 

iron is not clearly indicated, nor is its mode of segregation clear, but it is widely distributed in the anorthosite far from the active feeding channels, wlere a 

moderate temperature and a liquid phase are probable, 

though a gas-phase segregation from the parent rock is 

possible.

The foregoing outline of the most probable physicochemical processes controlling the segregation cf the 

mineralizing materials of the Roseland district from 

their parent magma is obviously a tentative explai ation 

of a difficult problem in mineral paragenesis. The 

chemical reactions of phosphorus and titanium in particular under high pressures and temperatures have not 

been studied. Experiments that would add greatly to 

our knowledge of the chemical reactions of thes^ elements and others of interest to students of ore deposits 

are possible, but the complex chemical environment and 

the physical conditions in a very deep-seated crystallizing magma can probably never be duplicated experimentally. It is evident that there are serious gaos in 

the fundamental knowledge required for a coirolete 

and rigorous explanation of the paragenetic processes. 

Many essential chemical and physical data are lacking, 

and mineralogic and geologic observations are only 

partly informative, as they do not reach to the deeper 

zones and can never directly reveal processes. For 

these reasons, speculative studies seem to be a legitimate 

mode of approach to the problem, provided both the 

writer and the reader clearly understand that the 

picture set forth is a tentative one.

The first test of any suggested paragenesis, of course, 

is whether it gives a consistent picture of the processes 

under consideration in the particular region, but a more 

rigid test is its applicability by other students to other
38 TITANIUM DEPOSITS OF NELSON AND AMHEKST COUNTIES, VIRGINIA

areas. The explanation must agree with geologic relations and physicochemical knowledge and must be 

checked by experiment wherever possible. If studies 

such as these are applied to numerous mineral provinces 

and modified where necessary to fit the geologic and 

physicochemical picture, the serious gaps in studies by

direct observation and experiment may be gradually 

filled in, and an acceptable story of mineralization 

processes built up, step by step. It is therefore as a 

trial approach to the intricate problems of mineral 

paragenesis that the foregoing study of the segregation 

of mineralizers has been presented.
PLATES 1-19

39

286089-41——5
PLATE 1

POLISHED SPECIMENS FROM THE MINE OF THE AMERICAN RUTILE CO. SHOWING RELATION OF PARTLY

GRANULATED FELDSPAR TO RUTILE

All natural size. Note the absence of rutile (round black grains) in the primary feldspar (gray material) in all the specimens.

A. The dark-gray areas represent primary feldspar; they are all in uniform optical orientation and so represent residual areas of a

single crystal. White, fine-grained, granulated feldspar has formed along fractures. 

B. The granulation is more complete than in A, and the residual areas of primary feldspar are more isolated; but all are in uniform

optical orientation. The greater granulation has been followed by the introduction of more rutile. 

C. Rounded residual areas of primary feldspar with abundant rutile in the granulated parts. 

D. Almost solid rutile (black) encloses residual areas of primary feldspar that shows a few small patches of granulation.

40
GEOLOGICAL, SURVEY PROFESSIONAL, PAPER 198 PLATE 1

* ••

*•••/
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 2
PLATE 2 

REPLACEMENT OF FELDSPAR BY SECONDARY MINERALS

A. Photograph of a polished specimen from mine of Dominion Minerals, Inc., on Piney River about a mile northwest of the Charlottesville-Lynchburg road. Finely granulated feldspar has been cut by a series of fractures, along which secondary minerals 

have formed. These are clinozoisite, sericitic muscovite, and tremolite. Natural size.

B. Photomicrograph of a thin section of feldspar from the mine of the American Rutile Co., cut from the specimen shown on plate 

1, A. The upper part shows nearly fresh primary feldspar cut by shear zones, along which granulation has occurred. In 

the lower part, where granulation has been nearly complete, secondary silicates (sericitic muscovite and clinozoisite) have 

formed; they show as small white grains, which are nearly absent in the primary feldspar. Crossed nicols. X 48.

C. Photomicrograph of a thin section of a specimen from the mine of the American Rutile Co. Two residual areas of single feldspar 

crystals contain disseminated grains of secondary silicates. The granular parts represent nearly complete replacement of 

feldspar by tremolite, clinozoisite, and sericitic muscovite. Black enclosing material is ilmenite. X 48.

D. Photomicrograph of a thin section of anorthosite from the mine of the American Rutile Co. The lower right part represents a 

strained but ungranulated area of antiperthitic feldspar. The remainder represents granulated feldspar and shows the great 

variation in the size of grain. These grains retain the antiperthitic structure of the primary feldspar. Near the top are 

abundant grains of secondary silicates, which are almost absent in the ungranulated material. Crossed nicols. X 48.

41
PLATE 3 

PHOTOMICROGRAPHS OF FELDSPATHIC ROCKS SHOWING REPLACEMENT BY SECONDARY MINERALS

A. Specimen from the mine of the American Rutile Co. The lighter part is andesine and the darker irregular veinlets are clinozoisite. X 28. 

B. Part of a single crystal of antiperthitic andesine from the mine of the American Rutile Co. The dark material-is ilmenite, which

has formed most abundantly along shear zones. X 48. 

C. Ungranulated feldspar from the mine of the American Rutile Co., similar to the material illustrated on plate I, A. The small

discontinuous lenses are microcline enclosed in andesine. Dark areas are secondary silicates. X 86. 

D. Specimen from a small aplitic dike at the Massies Mill School. Minute lenses of albite are enclosed in microcline. The mutual

relations of the two feldspars are the reverse of those shown on C. Near the lower left corner are two small grains of quartz,

and just above this is a small veinlet of quartz that follows a cleavage plane in the feldspar. X 36.

42
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 3
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 4
PLATE 4

PHOTOMICROGRAPHS OF THIN SECTIONS SHOWING REPLACEMENT OF FELDSPAR BY SECONDARY

MINERALS

A. Altered anorthosite from the mine of the American Rutile Co. The sheaflike groups of crystals are clinozoisite. Light-colored 

mottled material in the groundmass is tremolite and sericitic muscovite. A trace of the original antiperthitic structure of 

the feldspar shows as faint diagonal lines. X 86.

B. Altered anorthosite from the mine of Dominion Minerals, Inc., on Piney River 1 mile northwest of the Charlottesville-Lynchburg 

road. Black areas are pyrite of dendritic habit. Dark-gray areas are clinozoisite. The light-gray mottled material is 

white feldspar enclosing sericitic muscovite and tremolite. X 48.

C. Altered anorthosite from the mine of the American Rutile Co. Black areas are clinozoisite. Near the lower part is an area of 

badly corroded antiperthitic feldspar. X 48.

D. Material from a small lens in the nelsonite mine of the Southern Mineral Products Corporation. The light-colored central area 

is andesine, which has been replaced by hornblende along its right border. The dark grain near the upper left corner is a 

very fine grained aggregate of hornblende, which has completely replaced augite. The dark border is a reaction rim of finegrained clinozoisite. The white area in the lower left corner is the result of the breaking away of the fine-grained hornblende. X 36.

43
PLATE 5 

PHOTOMICROGRAPHS OF THIN SECTIONS SHOWING REPLACEMENT

A. Blue-gray rutilated quartz from the mine of the American Rutile Co. The section is cut perpendicular to the optical axis of the 

quartz. Note the large proportion of rutile needles that make an angle of 60° with one another. This distribution is symmetrical around the c axis of the quartz and evidently has been controlled by the trigonal symmetry of the quartz. The 

rutile needles are 0.3 to 0.5 microns in diameter, and some reach several millimeters in length. X 86.

B. Specimen from the mine of the American Rutile Co., which shows quartz (white areas) partly replaced by actinolite. Needles 

of actinolite extend into both areas of quartz. X 48.

C. Specimen from the mine of Dominion Minerals, Inc., on Piney River, about a mile northwest of the Charlottesville-Lynchburg 

road. Shows extensive replacement of anorthosite along a shear zone. The white area is quartz, the light-gray granular 

material is garnet and clinozoisite, and the black is pyrite. X 48.

D. Specimen from the mine of the Southern Mineral Products Corporation. Rutile has formed in anorthosite, and tonguelike areas 

seem to have extended out along nearly parallel fracture zones that are inclined about 45°. X 24.

44
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 5

D
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 6
PLATE 6 

PHOTOGRAPH OF A POLISHED SPECIMEN FROM THE MINE OF THE AMERICAN RUT1LE CO.

Shows replacement of anorthosite along a series of parallel fractures, forming a series of lenses. The dark-gray areas are clinohypersthene; the black is hornblende, an alteration product of the clinohypersthene. Rounded dark areas in feldspar (white) 

are ilmenite, but most of the ilmenite occurs in the dark-colored lenses where it does not show. A second, nearly vertical system 

of fractures makes angles of about 45° with the major fractures. The secondary fractures contain the alteration products of 

clinohypersthene near intersections, but for the most part they are filled with biotite. Natural size.

45
PLATE 7 

A POLISHED SPECIMEN FROM THE MINE OF THE AMERICAN RUTILE CO.

Shows replacement of anorthosite localized along shear planes. The dark areas are clinohypersthene and its alteration product 

hornblende. A secondary set of fractures makes angles of about 45° with the major fractures. Along these secondary fractures secondary silicates, largely biotite, have also formed. Dark, rounded areas are ilmenite. Natural size.

46
GEOLOGICAL, SURVEY PROFESSIONAL PAPER 198 PLATE 7
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 8
PLATE 8

PHOTOGRAPH OF A POLISHED SPECIMEN FROM THE MINE OF THE AMERICAN RUTILE CO.

Hornblende has replaced anorthosite along a system of parallel fractures. Numerous areas of blue-gray quartz are distributed 

throughout the specimen and are of a slightly darker gray than the feldspar. Some of these form distinct veins, but others are 

irregular or rounded masses. In many places the earlier quartz veins have been replaced by hornblende. Shear zones cut 

quartz as well as feldspar, and both contain hornblende. Thus the sequence of mineralization is feldspar, quartz, hornblende. 

Natural size.

47

28CAW—U—— 6
PLATE 9

TWO POLISHED SPECIMENS FROM THE MINE OF THE AMERICAN RTJTILE CO. SHOWING REPLACEMENT

Natural size

A. Large partly replaced crystal of clinohypersthene. Granular light-gray areas are apatite, white area at the top is quartz. Just 

to the left of the center and between the two apatite areas is a large grain of ilmenite. The clinohypersthene has been partly 

replaced along the cleavage planes, which are nearly horizontal, by hornblende and ilmenite.

B. The dark-gray area is composed of clinohypersthene that has been partly replaced by hornblende (black). Ilmenite (not visible) 

has formed within the hornblende veins. Two areas of pyrrhotite (P) occur near the lower margin. Veinlets of secondary 

minerals have formed along fractures in the feldspar.

48
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 9
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 10
PLATE 10 

PHOTOGRAPH OF A POLISHED SPECIMEN OF INJECTION GNEISS

Taken near the contact between the schistose country rock and the anorthosite, on the bank of Tye River about a mile southeast of 

Massies Mill. The dark-gray areas are partly mineralized and distorted schist. White areas are feldspar composed dominantly 

of perthitic microcline. The introduced minerals in the dark-colored schistose areas are ilmenite, dark-blue quartz (Q), amphiboles, and biotite. A later system of shear zones, which consist essentially of sericitic muscovite, bend around the feldspar 

grains and cut diagonally across them. Black areas within feldspar are ilmenite. Natural size.

49
PLATE 11

PHOTOGRAPH OF A POLISHED SPECIMEN FROM THE OLD MINE OF THE GENERAL ELECTRIC CO. ON PINEY 

RIVER SHOWING REPLACEMENT OF ANORTHOSITE BY NELSONITE

The left and lower parts of the specimen are anorthosite consisting of granulated feldspar (F) that contains abundant minute disseminated grains of secondary silicates. The central area is similar but is completely surrounded by apatite (A). At the extreme 

right is nelsonite (AO, composed of apatite and rutile. The medium-gray irregular areas or veinlets within the feldspar are 

largely secondary silicates, of which clinozoisite (Z~) is dominant. The right-hand part is granular nelsonite. The dark-gray 

areas at the top and to the left of the central mass of anorthosite are almost pure apatite, and apatite forms stringers that project 

far into the feldspar areas. Commonly the broader parts of stringers are apatite or apatite with a few rutile grains; and the 

narrow parts of the stringers are clinozoisite and associated secondary silicates. At the extreme right is a residual mass of 

anorthosite impregnated with apatite and rutile. Near the top there are gradations from apatite to feldspar rock. Natural size.

50
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 11
GEOLOGICAL STTRVKY PROFESSIONAL PAPER 198 PLATE 12
PLATE 12 

PHOTOGRAPHS OF POLISHED SPECIMENS SHOWING REPLACEMENT

A. Specimen from the mine of the American Rutile Co. at Roseland. Near the center is a veinlike area of nelsonite (apatite and 

ilmenite) with ilmenite concentrated along the border. Numerous areas of ilmenite (black) are scattered through feldspar 

(white). Near the bottom ilmenite has formed along small fractures that make an angle of about 45° with the large vein. 

Near the right and lett sides are residual areas of fractured primary feldspar enclosed in granulated material. One-half 

natural size.

B. Blue-gray quartz from the Bryant farm on Alien Creek with irregular areas of apatite (white). The contrast is produced by etching the apatite. Natural size.

51
PLATE 13 

AMPHIBOLITE NELSONITE REPLACING ANORTHOSITE

A, B, and C. Photomicrographs of amphibolite nelsonite from the Bryant farm on Alien Creek. Black areas in A are elongated 

stringers of ilmenite that cut through the fine-grained felted aggregate of hornblende. White areas are apatite. The specimen represents a more advanced replacement of material illustrated in C. X 48. B shows thick augen-shaped, residual 

masses of anorthosite enclosed in a fine-grained aggregate of hornblende and its alteration products. The diagonal orientation of the augen of residual feldspar was controlled by shear zones. The darker material represents zones of more intense 

shearing. X 48. The white area in C is part of residual augen of feldspar similar to those shown in B. The granular 

material along the border of the feldspar augen is fine-grained colorless garnet. X 86.

D. Photomicrograph of hornblende-rich nelsonite from the mine of the Southern Mineral Products Corporation. The lightcolored areas marked a are apatite, and the black areas are ilmenite. The elongated augen -are sheared, recrystallized, and 

partly replaced residual aggregates that were originally feldspar. They are surrounded by zones along which shearing has 

been most intense and along which nearly pure hornblende has formed. The small white area at the lower left corner is an 

air bubble. X 36.

52
GEOLOGICAL SUEVEY PEOFESSIONAL PAPER 198 PLATE 13
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 14

D
PLATE 14

A. Photomicrograph of a thin section of nelsonite from the property of the American Lead Co. on the Bob Kite farm about a mile 

north of Roseland. Apatite (gray) is cut by veinlets of ilmenite (black). X 48.

B. Photomicrograph of a polished specimen of nelsonite from Alien Creek, about half a mile west of Rose Union. Shows the rounding of apatite grains (white) and their embayment by ilmenite (black). X 10.

C. Photomicrograph of a specimen from the mine of the Southern Mineral Products Corporation. The light-colored partly rounded 

grains are apatite. The groundmass is largely fine-grained biotite which has formed by the replacement of feldspar. Near 

the upper right-hand corner and along the left margin are residual areas of only partly replaced feldspar with the perthitic 

structure preserved. Black areas are ilmenite. X 24.

D. Photomicrograph of a thin section of a large crystal of clinohypersthene from the mine of the American Rutile Co. The dark 

areas are ilmenite, which has formed abundantly along two fractures. Near the top are elongated lenses of ilmenite that 

has formed in the cleavage planes of the clinohypersthene. These lenses arc so thin that they transmit light and are lavender 

purple in color. X 48.

53
PLATE 15

PHOTOMICROGRAPHS OF LEAN NELSONITE FROM THE MINE OF THE SOUTHERN MINERAL PRODUCTS CO.

SHOWING REPLACEMENT OF ANORTHOSITE BY NELSONITE

In all specimens the white areas are apatite and the black ones are ilmeiiite

A. Residual grain of antiperthitic feldspar near the center. This is enclosed in a biotite-actinolite aggregate that has completely

replaced feldspar. X 86. 

B. Similar material with a partly replaced feldspar grain in the lower part. Replacement, which has followed the perthitic lenses,

has partly preserved the structure. X 86. 

C. Photomicrograph of hornblende-rich nelsonite. The central area is a lens of andesine that has escaped replacement, although

most of the specimen is similar to the augenlike areas shown in D. At the right of the main andesine mass are isolated areas

of andesine separated by shear zones. Gray area at the upper right corner is apatite. X 86. 

D. Several striated grains along the lower right side represent partly replaced feldspar grains. Ghostlike outlines of the totally

replaced feldspar grains are faintly discernible throughout the specimen. The groundmass is biotite and actinolite. X 48.

54
GEOLOGICAL SURVEY

PROFESSIONAL PAPER 198 PLATE 15
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 16
PLATE 16

PHOTOGRAPHS OF POLISHED SPECIMENS SHOWING REPLACEMENT

Natural size

A. Specimen from the mine of the American Rutile Co. The feldspar has been very thoroughly granulated and cut by a system of 

fractures along which the secondary silicates clinozoisite, tremolite, and sericitic muscovite have formed. Black areas are 

rutile. Note the tendency for rutile to be associated with areas of extreme alteration of feldspar or with small fractures.

B. Part of one of the anorthosite lenses in schistose country rock on the south border of the anorthosite mass at Rose Mills. Photographed in reflected light. The white areas are rutile. Near the right side are numerous rounded or elongated and sharply 

bounded areas of rutilated quartz. White cloudlike areas are slightly altered feldspar, and the darker gray is feldspar that 

has been largely replaced by secondary silicates. Black areas are shear zones filled with clinohypersthene and its alteration 

products.

55

286089—41-
PLATE 17

A, B, and C. Photomicrographs, by reflected light, of polished specimens of clinohypersthene from the mine of the American Rutile 

Co. Dark-gray areas are quartz, the white areas are ihnenite, and the black roughly horizontal areas are fractures, enclosing 

clinohypersthene. A and B show quartz and ilmenite that have formed broad veinlets in the cleavage planes of clinohypersthene. 

The very narrow veinlets are rutile. Diagonal lines are due to polishing. C is a large mushroomlike vein of quartz with grains 

of ilmenite cutting across the cleavage of a clinohypersthene crystal. X 16.

D. Thin section of a rounded grain of apatite enclosed in ihnenite and cut by fractures in which ilmenite has formed. X 48.

56
GEOLOGICAL SURVEY PROFESSIONAL PAPER 188 PLATE 17
GEOLOGICAL SURVEY PROFESSIONAL PAPER 198 PLATE 18
PLATE 18 

PHOTOMICROGRAPHS OF THIN SECTIONS SHOWING REPLACEMENT. X 24

A and B. Crystals of rutile enclosed in anorthosite from the mine of the American Rutile Co. The gray inner part is rutile and the

black along the outer border and along fractures is ilmenite that has replaced rutile. The light-colored, nearly

white border material is sphene "leucoxene." 

C and D. Biotite nelsonite from the Bob Kite farm about a mile north of Roseland. The white areas are apatite that has been

fractured and the fractures filled with later minerals. The gray veinlets are biotite and the black ones ilmenite.

The gray areas in the groundmass are also biotite.

57
PLATE 19

PHOTOGRAPHS OF SPECIMENS FROM THE ROSELAND AREA SHOWING REPLACEMENT

A and B. Polished specimens of rutile nelsouite from the Giles property, a quarter of a mile west of Roseland. The white veinlets 

are sphene "leucoxene" that has formed by replacement of rutile (black) along fractures. The gray, horizontal areas in B 

and the diagonal area extending across A represent zones of close shearing. The white area on the right of A is partly 

replaced anorthosite. In the lower half of B several gray, only slightly elongated areas are apatite. X 3.

C. Thin section showing irregular tonguelike areas and isolated grains of rutile (black) that have formed in anorthosite (white background). The gray areas are sphene. X 8.

D. Thin section of rutile (light gray) with ilmenite (black) that has formed along fractures. Still later sphene has replaced both 

rutile and ilmenite. X 40.

58
GEOLOGICAL, SURVEY PROFESSIONAL PAPER 198 PLATE 19

D

INDEX

Abstract___— _—— — — __ — —__ _ ___ _ __________________—._____ i

Acknowledgments.._....._.._____ —___ _.____ —________________ _ 1-2

Actinolite, mode of occurrence of._..—__ _ ______________________ 8,19, pis. 2-4

Albitization, physicochemical processes controlling_________________________ 27

Alumina and alkalies, relation between,__________________..______ 27-28

Amphiboles, distribution and properties of____________ 12-13, pis. 4, D, 9, 13, 15, C

Analyses___. — _ — __________________________________________ 10-15

Andesine, antiperthitic, optical properties of ___________________ _ 10, 16, pi. 3, C

paragenesis of_—____________...___________________ 22 (insert)

Anorthosite, andesine, occurrence and origin of..______________________________ 3,16

border facies of—. —_—- ——_ — — _ — — ___-_—___ — __ —____________ 4,17

oligoclase, occurrence and origin of__. ___ ____________________________ 4,17

Apatite, distribution and chemical character of__ ____________ 14, pi. 12, B 

slsof- ———— — — —— — — — — —— 18, 22 (insert), pis. 9, A, 12, B

Balk, Robert, quoted__ __----------_---_-_---__--._-----_-_-_-.________ 16

Bowen, N. L., quoted__.————-________—__—___—-_——_____ 27,28-29

Brush, G. J., and Smith, J. L., analysis by.___________..._____ 12

Buddington, A. F., quoted..-----____...____.._______________ 16

Calcite, distribution of_____ _ _______________............ -.__._____ _ 15

Calcium, segregation of__. ._._._—_______.___.___.________________ 36-37

Charlevoix district, Quebec, titanium deposits of..__. — — _-....„--_....._. 23

Clinohypersthene, optical and chemical properties of__-._____-___-_______ 11, pi. 9

paragenesis of—________________ ———...._..__...-._..._______ 22 (insert)

Clinozoisite, optical and chemical properties of__-.______._ 11-12, pis. 3, A, and 4, A

paragenesis of—— — ———— ————_________ 19, 22 (insert), pis. 2-4

Cobalt-bearing clay, occurrence and chemical character of__ __--.----_--___. 15

Dikes, ferromagnesian, origin of_ 

Eskola, Pentti, quoted ________

18

27

Fairchild, J. G., analyses by._ _______ __________ _________________ 10,11,12,13,33

Feldspar, optical and chemical properties of___________________ 10-11, pis. 3, C, 10

Fenner, C. N., quoted_____ _ _______________.._._..._.....____..._.._. 27,29

Ferromagnesian lenses. See Lenses.

Ferromagnesian rocks, character of_ __--------__-.____-__-_____-__-__.________ 6-7

Qillson, J. L., quoted--- — ——- — — — — — — - ——— . —— —— —— — 23

Gneiss, injection, origin of. ————— - — - — —— —- — — — ~ 17-18, pi. 16, B 

Graphite, occurrence and character of__...._—— — — — — ———— — — — — — — 14-15

Ilmenite, distribution and character of_..____________ _ 14, pis. 13, A, 14, A

paragenesis of. .___-___ 18-19, 22 (insert), pis. 9, A, 13, 14, 15, 18, A, B, C, 19, D 

Ilmenite nelsonite, mineral composition of_.__-___ — _— — _ — -___ — — -__ — — 7-9,

pis. 4, D, 13 14, A, B, C, 15, 17, D, 18, C, D 

Iron, segregation of_______________________ — .. — ._... ___________________ 36-37

Location of the area. ______—___-__--___--__________ —_________________ _ 2

Lenses, ferromagnesian, origin and relations of ________ — — — — — — _—__ — 19-20,

pis. 5, B, 6-9, 14, D, 16, B, 17, A, B, C 

Lovingston granite gneiss. See Quartz monzonite. 

Lynchburg gneiss, relations of..----. —------------ — -_-_-__._ — — ________ 2

Magmatic segregation, factors influencing— _________ ________ _ _ _________ 27-38

Magnesium, segregation of.__—— —— —— ——___________ —— ____.___. 36-37

Magnet Cover, Ark., titanium deposits of—— _ — __-________.______— — 23-26

Magnetite, character and relations of-- — - — — ——————. — -----------—— 14

Manganese, occurrence of.——_._-_-_-—- ———— ————— — — - — — — 15

Mawdsley, J. B., quoted.-.-——__—————————————. ———— -———— 23 

Mica, distribution and character of_.--___———-———.——-— 13, p\ 18, C, D

paragenesis of—___-____-____.—-._-.___ 19, 22 (insert,), pis. 2-4 

Mineralization, physicochemical processes controlling_... — --—__ — -_——_ 26-38 

Minerals, physicochemical processes controlling paragenesis of..——————— 26-38

sequence of________——__ — _______ — ——— - — —— —— -------— 22 (insert)

See also individual minerals.

Nelsonite, distribution and character of__———- — _..-__——-_. ——— — — 7-10,

pis. 4, D, 13, 14, A, B, C, 15,17, D, 18, C, D, 19 

paragenesis of————— 20-22, pis. 11,12, A, 13,14, A, D, 15,17, L, 18, C, D

Origin of the rocks and minerals_...-. —— —— ——— —— — — — — __- —— — 15-22

Osborne, F. F., quoted.-———————.——_._ —————..__———._ 23

Paragenesis of titanium minerals....——————————.—— 22,22 (insert), 37-38

See also individual rocks and minerals.

Pegmatite-aplite zones, features of— — —————— - ————————— — — 6 

Petrography, features of_-_-_____ ———————— -——————-————— 3-10 

Phosphorus, magmatic segregation of.—- ——— —— — —— ——— — ——— 34-35,37

Pre-Cambrian rocks, distribution and character of—————— —— —— ——— 2-3

Pyrite, character and relations of__---------—-------————— 15, pis. 4, B, 9, B

Pyrrhotite, character and relations of_.. —————... —————————— _. 15

Quartz, paragenesis of. ____________._._-. ———...._— 17, 22 (insert), pi. 16, B

rutilated, distribution and character of_ ————____.„. 11, pis. 5, A, 12, B 

Quartz lenses, distribution and character of.——— _.-._. ——— ———————— 7,17 

Quartz monzonite, distribution and character of------_—————————— 2-3

Reaction principle, discussed____ _ _—_—___ ——.——. — —.—. ————.. 27

Replacement of minerals, chemistry of-— ——— ———— - — —— ——————— 30-33

specimens showing.-. ................................................. pis. 1-19

Replacing solutions, character of__————————————— ....———————— 28-30

Roseland anorthosite, distribution, character, and relations of. 2-6, pis. 1-3,10,16, B 

Rutile, distribution and chemical character of__—_...._——. 13-14, pi. 18, C

paragenesis of.------------- 18-19,22 (insert), pis. 1, 5, A, 11,18,^4, B, 19, D

Rutile nelsonite, character of_.__...—————------- ———.——— 9-10, pi. 19

St. Urbain, Quebec, titanium deposits of__. 

Scope of the report----..-- —— ——— — —— 

Smith, J. L., and Brush, G. J., analysis bySphalerite, occurrence of__---_-— — — —— _.

———— —— ——————— 23

_... — —— „— .......—. 1

—————— —— -————— 12

—— —— ——— — ————— — 15

Sphene, distribution and chemical character of-.--------- —— _______—— 14, pi. 19

Stability of minerals, physicochemical processes influencing.—....._ —. —.. 26-27

Stevens, R. E., analysis by.._:._._.—.————. —.. —— —._._._ — _-____._ 14

Taber, Stephen, and Watson, T. L., quoted...—— ------- —— -__ ——._ — ___ 3

Thornton, W. M., Jr., analyses by.———————___—————_________ 12,14

Titanium, segregation of—-——---------- — — ___- — ————— — — ___.__ 35-36,37

Tremolite, mode of occurrence of -__— — — — — — — — —— — — — __ 19, pis. 2-4

Washington, H. S., analyses by.___———... 

Watson, T. L., and Taber, Stephen, quoted. 

Wells, R. C., analysis by..- ——. —.——— 

Williams,!. F., quoted———_———......

286089—41——8 59

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