Mineralogy and Geology of 

the \Vkgnerite Occurrence 

co Santa Fe Mountain, 

Front Range, Cobrado

GEOLOGICAL SURVEY PROFESSIONAL PAPER 955
Mineralogy and Geology of 

the Wignerite Occurance 

on Santa Fe Mountain, 

Front Range, Colorado

By DOUGLAS M. SHERIDAN, SHERMAN P. MARSH, 

MARY E. MROSE, and RICHARD B. TAYLOR

GEOLOGICAL SURVEY PROFESSIONAL PAPER 955

A detailed mineralogic study of wagnerite, a rare phosphate 

mineral occurring in the report area in Precambrian gneiss; 

this is the first recorded occurrence of wagnerite in the 

United States

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Main entry under title:

Mineralogy and geology of the wagnerite occurrence on Santa Fe Mountain, Front Range, Colorado.

(Geological Survey Professional Paper 955)

Includes bibliographical references.

1. Wagnerite Colorado Santa Fe Mountain. 2. Geology Colorado Santa Fe Mountain.

I. Sheridan, Douglas M., 1921- II. Series: United States Geological Survey Professional Paper 955.

QE391.W3M56 549'.72 76-10335

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, B.C. 20402 

Stock Number 024-001-02844-1
CONTENTS

Metric-English equivalents ..............................

Abstract............................................................

Introduction.....................................................

Acknowledgments............................................

Geologic setting...............................................

Occurrence.......................................................

Descriptive mineralogy....................................

Methods used for optical determinations.

Page

1

1

2

2

3

5

5

Descriptive mineralogy Continued

Wagnerite...............................................

Other minerals.......................................

Mineral assemblages and textural relations.

Chemistry......................................................

X-ray crystallography...................................

Origin............................................................

References cited.............................................

Page

5

8

11

14

15

19

22

ILLUSTRATIONS

Page 

FIGURE 1. Map of east-central Front Range showing Santa Fe Mountain wagnerite locality and location of figure 2.................................. 2

2. Map showing distribution of rutile-bearing light-colored gneisses in the Santa Fe Mountain-Beaver Brook-Soda

Creek area ...................................................................................................................................................................................^ 3

3. Geologic map of wagnerite locality, Santa Fe Mountain ................................................................................................................. 4

Photomicrographs:

4. Large ameboid-shaped grain of wagnerite...................................................................................................................... 6

5. Large blocky grain of wagnerite poikiloblastically enclosing rows of rutile grains..................................................... 7

6. Complex intergrowth of closely spaced grains of wagnerite and plagioclase............................................................... 7

7. Part of a large wagnerite grain that is crowded with tiny inclusions ........................................................................... 8

8, 9. Rims of apatite on wagnerite.......................................................................................................................................... 8, 9

10. Prismatic to blocky inclusions of apatite in wagnerite.................................................................................................. 9

11, 12. Wagnerite strongly oriented parallel to foliation defined by fibrolitk sillimanite....................................................... 11, 12

13, 14. Prismatic sillimanite cutting wagnerite and other minerals.......................................................................................... 12, 13

15. Corundum containing numerous needles of sillimanite................................................................................................ 13

16. Corundum and rutile along grain boundaries of wagnerite.......................................................................................... 13

17. X-ray powder photographs of wagnerite, ferroan wagnerite, magniotriplite, and triplite........................................... 20

TABLES

Page 

TABLE 1. Modes of light-colored gneisses, Santa Fe Mountain wagnerite locality, Colorado......................................................................... 5

2. Optical data for wagnerite from Santa Fe Mountain, Colorado....................................................................................................... 5

3. Comparison of optical data for wagnerite......................................................................................................................................... 5

4. Optical data for other minerals from wagnerite locality, Santa Fe Mountain, Colorado................................................................ 10

5. Chemical analyses of wagnerite ......................................................................................................................................................... 14

6. Microprobe analysis of wagnerite from Santa Fe Mountain, Colorado............................................................................................ 15

7. Crystallographic, compositional, and density data compared for wagnerite, ferroan wagnerite,

magniotriplite, and triplite......................................................................................................................................................... ig

8. X-ray powder diffraction data for wagnerite, Mg2(PO4 )F................................................................................................................. 17

III
IV CONTENTS

METRIC-ENGLISH EQUIVALENTS

Metric unit English equivalent

Length

millimetre (mm) 

metre (m) 

kilometre (km)

= 0.03937 inch (in) 

= 3.28 feet (ft) 

= .62 mile (mi)

Area

square metre (m2 ) 

square kilometre (km2 ) 

hectare (ha)

= 10.76 square feet (ft2 ) 

= .386 square mile (mi2 ) 

= 2.47 acres

Volume

cubic centimetre (cm3 ) 

litre (1) 

cubic metre (m3 ) 

cubic metre 

cubic hectometre (hm3 

litre 

litre 

litre 

cubic metre

cubic metre

= 0.061 cubic inch (in3 ) 

= 61.03 cubic inches 

= 35.31 cubic feet (ft3 ) 

= .00081 acre-foot (acre-ft) 

= 810.7 acre-feet 

= 2.113 pints (pt) 

= 1.06 quarts (qt) 

= .26 gallon (gal) 

= .00026 million gallons (Mgal or 

10« gal) 

= 6.290 barrels (bbl) (1 bbl = 42 gal)

Weight

gram (g) 

gram 

tonne (t) 

tonne

= 0.035 ounce, avoirdupois (oz sivdp) 

= .0022 pound, avoirdupois (Ib avdp) 

= 1.1 tons, short (2,000 Ib) 

= .98 ton, long (2,240 Ib)

Specific combinations

kilogram per square 

centimetre (kg/cm2) 

kilogram per square 

centimetre 

cubic metre per second 

(mVs)

= 0.96 atmosphere (atm) 

= .98 bar (0.9869 atm) 

= 35.3 cubic feet per second (ft3/s)

Metric unit

Specific

litre per second (1/s) 

cubic metre per second 

per square kilometre 

[(m»/s)/km2 ]

metre per day (m/d)

metre per kilometre 

(m/km) 

kilometre per hour 

(km/h) 

metre per second (m/s) 

metre squared per day 

(m2/d)

cubic metre per second

(mVs)

cubic metre per minute 

(rn3/min)

litre per second (1/s) 

litre per second per 

metre [(l/s)/m]

kilometre per hour 

(km/h) 

metre per second (m/s) 

gram per cubic 

centimetre (g/crn3 ) 

gram per square 

centimetre (g/cm2 ) 

gram per square 

centimetre

English equivalent

combinations Continued

= .0353 cubic foot per second

square mile [(fts/s)/rni2 ] 

= 3.28 feet per day (hydraulic 

conductivity) (ft/d)

= 5.28 feet per mile (ft/mi)

= .9113 foot per second (ft/s) 

 3.28 feet per second

= 10.764 feet squared per day (ft2/d) 

(transmissivity)

= 22.826 million gallons per day 

(Mgal/d)

= 264.2 gallons per minute (gal/min) 

= 15.85 gallons per minute

= 4.83 gallons per minute per foot 

[( gal/min) /ft]

 .62 mile per hour (mi/h)

= 2.237 miles per hour 

= 62.43 pounds per cubic foot (lb/fts) 

 2.04S pounds per square foot (lb/ft2)

 .0142 pound per square inch (lb/in2)

Temperature

degree Celsius (°C) 

degrees Celsius 

(temperature)

= 1.8 degrees Fahrenheit (°P) 

= [(l.SX°C)+32] degrees Fahrenheit
MINERALOGY AND GEOLOGY OF THE WAGNERITE OCCURRENCE 

ON SANTA FE MOUNTAIN, FRONT RANGE, COLORADO

By DOUGLAS M. SHERIDAN, SHERMAN P. MARSH, 

MARY E. MROSE, and RICHARD B. TAYLOR

ABSTRACT

The first known occurrence in the United States of wagnerite, a rare 

magnesium fluophasphate, is on Santa Fe Mountain near Idaho Springs 

in the Colorado Front Range. Wagnerite occurs as a minor constituent of 

thin lenses of sillimanite-plagioclase gneiss of Precambrian age. Other 

minerals in the gneiss are corundum, rutile, pale-brown biotite, apatite, 

monazite, zircon, and tourmaline. The sillimanite-plagioclase gneiss is a 

local lithologic variant of a persistent layer of rutile-bearing sillimanitequartz gneiss and related rocks that has been traced 13 km along a ~L>- 

shaped fold southeastward from the northern flank of Santa Fe 

Mountain.

The wagnerite from Santa Fe Mountain is anhedral, mostly fine 

grained, and pale yellow to yellowish tan. Luster is vitreous to slightly 

resinous. Cleavage (100) is very poor. In transmitted light, grains are 

colorless and nonpleochroic. The indices of refraction and the optic 

angle show a range in values: a =1.565-1.571, /?= 1.567-1.5 72, 

7=1.578-1.585 (all ± 0.002); (+)2F=28°-33° (±1°). Dispersion is r>v, 

weak.

Textural relations indicate that a single stable mineral assemblage 

characterizes the sillimanite-plagioclase gneiss: wagnerite+plagioclase 

(albite)+fibrolitic sillimanite+magnesian biotite. To this assemblage 

may be added small amounts of rutile, monazite, zircon, and apatite, 

minerals inferred to represent phases belonging to a relatively early stage 

of crystallization during high-grade regional metamorphism. 

Corundum, prismatic sillimanite, and some apatite crystallized later but 

probably during the same regional metamorphism.

Chemical analysis of the wagnerite from Santa Fe Mountain led to 

the formula (Mg,Fe,,Mn) 203 PO4 (F,Cl) 096 , with Mg:Fe:Mn= 

0.97:0.02:0.01; this formula is close to the empirical formula 

Mg2<P04)F.

Single crystal X-ray-diffraction studies showed that the wagnerite from 

Santa Fe Mountain is monoclinic, space group P2i/a, with 

a=11.9263±0.0007 A, fe=12.6707±0.0008 A, c=9.641 1±0.0005 A, 

/?=108.283°±0.005°, volume =1,383.37 As. Specific gravity calculated 

from refined cell data is 3.16 g/cc; specific gravity measured by the 

pycnometer method is 3.13 g/cc. A strong monoclinic subcell is present 

with the fc-axis halved (6.335 A); the subcell is in space group 72/a with 

Z=8, and its cell parameters are comparable with those reported in the 

literature for triplite-group minerals. The X-ray powder-diffraction 

pattern taken in Fe/Mn_radiation has the following strong lines (hkl, d, 

I): 141, 2.970 A (100); 402, 2.839 A (85); 202, 3.114 A (60); 122, 3.287 A 

(60); 023, 2.748 A (30); 421, 2.697 A (21).

A comparison of crystallographic data for wagnerite, ferroan 

wagnerite, magniotriplite, and triplite indicates that, despite their high 

magnesium content, ferroan wagnerite and magniotriplite are members 

of the triplite group and have a true cell that is different from that of 

wagnerite. So-called "ferroan wagnerite," from Hallsjoberget, Sweden, 

and from the Albe'res massif, eastern Pyrenees, France, is actually

magniotriplite; this material should not be referred to as ferroan 

wagnerite. Although X-ray powder-diffraction patterns of ferroan 

wagnerite and magniotriplite resemble the diffraction pattern of 

wagnerite, the pattern for wagnerite has a line at 5.66 A which 

distinguishes it from triplite-group minerals.

Rutile-bearing gneisses in the east-central Front Range are believed to 

have formed by metamorphism of bentonitic clays that were generated 

during intense weathering of intermediate to basic tuffs and flows in Precambrian time. The clays were partly reworked by surface waters; 

fluorine of probable volcanic source was adsorbed locally. After a thick 

succession of interlayered volcanic and sedimentary rocks accumulated, 

high-grade regional metamorphism took place. The thin layers and 

lenses of reworked weathered materials recrystallized to form rutilebearing sillimanite-quartz gneiss and related feldspathic rocks. 

Wagnerite formed locally, instead of apatite, where the amount of 

calcium was insufficient to accommodate the available phosphate.

INTRODUCTION

Wagnerite, a rare magnesium fluophasphate mineral, 

occurs as a minor constituent of thin layers of rutilebearing gneiss in regionally metamorphosed rocks of Precambrian age on the northern flank of Santa Fe Mountain, 

3.5 km southeast of Idaho Springs in the east-central Front 

Range, Clear Creek County, Colorado (fig. 1). This is the 

first recorded occurrence of wagnerite in the United States 

(Sheridan and others, 1971).

Sheridan and Marsh examined the Santa Fe Mountain 

area in 1968 during field investigation of rutile-bearingr 

gneisses in this region. Petrographic studies of rock 

samples from this area subsequently disclosed the presence 

of an unknown biaxial positive mineral that has a small 

optic angle. Optical, X-ray, and chemical investigations 

proved this mineral to be wagnerite. Additional samples 

were obtained by Sheridan and Marsh in 1969 and a 

geologic map of the wagnerite locality was prepared (fig. 

3).

This report describes the occurrence and properties of 

wagnerite from Santa Fe Mountain, Colo. Also included 

are descriptions of other minerals and the mineral 

assemblages, a comparison of the optical, chemical, and 

X-ray data for Colorado wagnerite with data for wagnerite from other localities in the world, and a discussion of
WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

105° 00'

39° 30'

0 10 20 KILOMETRES 

I__________I__________I

FIGURE 1. Map of east-central Front Range showing Santa Fe Mountain wagnerite locality (black square) and location of figure 2.

origin of the Colorado wagnerite. Responsibilities and 

credits are: Sheridan and Marsh provided the geologic 

field data and, together with Taylor, determined the 

descriptive mineralogy, petrography, and mineral 

assemblages; Mrose provided detailed X-ray data, 

discussions of the chemistry and X-ray crystallography, 

and comparison of wagnerite with ferroan wagnerite, 

magniotriplite, and triplite.

ACKNOWLEDGMENTS

We wish to thank Cabins, Inc. of Wheatridge, Colo., for 

its cooperation in permitting us to sample and study this 

wagnerite occurrence on their property. It is pertinent to 

mention that although wagnerite is a rare mineral, neither 

the wagnerite nor the corundum, which also occurs at this 

locality, can be regarded as having special museum or 

specimen value. These minerals are minor constituents of 

a metamorphic rock and, as such, are important to the geologist as unusual mineral phases in an uncommon metamorphic assemblage rather than to a mineral collector.

We are grateful to numerous U.S. Geological Survey 

colleagues for their help during this study. John W. 

Adams, George A. Desborough, Fred A. Hildebrand, and 

James M. Nishi made microchemical and other tests 

during the early part of the investigation. Laura E. 

Reichen provided the quantitative chemical analysis, 

Johnnie Gardner provided a fluorine determination, and 

Robert B. Finkelman made a microprobe analysis. Ray E. 

Wilcox, Irving J. Witkind, and Glenn A. Izett gave helpful 

advice during petrographic determinations of optical

data. Judith Konnert calculated the powder pattern for 

wagnerite from near Werfen, Austria, and also carried out 

least-squares analysis of the Colorado wagnerite.

All specimens used in these investigations, except those 

from the Colorado locality, were kindly supplied by 

several individuals: ferroan wagnerite from eastern 

Pyrenees by Francois Fontan of the Laboratoire de 

Mineralogie-Cristallographie (Toulouse, France); type 

magniotriplite, by Dr. Prof. G. Barsanov of the Fersman 

Mineralogical Museum (Leningrad, U.S.S.R.); and all 

other study materials, by Paul Desautels of the U.S. 

National Museum (Washington, D. C.).

GEOLOGIC SETTING

The wagnerite locality lies in the east-central part of the 

block of uplifted Precambrian rocks that form the core of 

the Colorado Front Range. Bedrock in the general vicinity 

of the occurrence is composed of a thick folded succession 

of gneisses of high metamorphic grade. These interlayered metasedimentary and metavolcanic rocks contain 

mineral assemblages in general correlative with the sillimanite zone and the upper part of the amphibolite facies. 

The regional metamorphism accompanied a long Precambrian period of deformation that involved two stages 

of plastic folding. Tight to open west-northwest-trending 

folds were formed first and, in some areas, were modified 

subsequently by more northerly trending crossfolds. 

Although granitic plutons were emplaced in this general 

region during three major periods of igneous activity in 

the Precambrian Era, the closest major igneous bodies are 

more than 5 km from the wagnerite locality. The geologic 

setting, therefore, is regional metamorphic rather than 

contact metamorphic.

Feldspar-rich gneiss (chiefly plagioclase, quartz, microcline, and biotite) and biotite gneiss (chiefly biotite, 

plagioclase, and quartz) are the principal metamorphic 

rocks in the east-central Front Range. Much of the biotite 

gneiss is sillimanitic, and some contains garnet-bearing 

and cordierite-bearing layers. Interlayered with the 

feldspar-rich gneiss and the biotite gneiss are variable 

amounts of hornblende gneiss, amphibolite, and calcsilicate gneiss.

Thin layers and lenses of rutile-bearing light-colored 

gneisses occur at several stratigraphic levels within this 

thick succession of gneisses. These range in thickness from 

15 cm to 30 m and contain from trace amounts to about 5 

percent of rutile. A remarkably persistent layer has been 

traced along a Z-shaped fold for about 13 km southeastward from the northern flank of Santa Fe Mountain 

(fig. 2). The distribution of the rutile-bearing gneisses and 

other Precambrian rocks in the east-central Front Range is 

shown in a generalized map by Marsh and Sheridan (1976, 

fig. 2).
OCCURRENCE

105°22'30"

Trace of rutile-bearing light-colored 

gneisses Dashed where approximately located

Fault Dashed where inferred

Wagnerite locality

\ 2 3 KILOMETRES

FIGURE 2. Map showing distribution of rutile-bearing light-colored gneisses in the Santa Fe Mountain-Beaver Brook-Soda Creek area.

The rutile-bearing light-colored gneisses are composed 

of several lithologic varieties that are interlayered and 

gradational along strike. The most common varieties are 

sillimanite-quartz gneiss, biotite-quartz-plagioclase 

gneiss, and rocks gradational between these two types. 

Less common regionally, but locally predominant, is a 

sillimanitic topaz-quartz gneiss (Sheridan and others, 

1968), which is present in several localities between Santa 

Fe Mountain and the eastern margin of the Front Range. 

At Santa Fe Mountain a local variant of the rutile-bearing 

light-colored gneisses is a sillimanite-plagioclase gneiss 

containing wagnerite and corundum.

OCCURRENCE

At the Santa Fe Mountain wagnerite locality, rutilebearing light-colored biotite-quartz-plagioclase gneiss 

forms two northwest-trending layers that are separated by 

hornblende gneiss (fig. 3). Wagnerite occurs in a 

corundum-bearing sillimanite-plagioclase gneiss that 

forms a lens within the biotite-quartz-plagioclase gneiss

in the eastern layer and that interfingers with biotitequartz-plagioclase gneiss in the western layer. Small 

bodies of simple quartz-feldspar pegmatite intrude the 

succession of metamorphic rocks here as they do 

ubiquitously throughout the Precambrian terrane of the 

east-central Front Range.

Although rutile-bearing gneisses at this stratigraphic 

level persist continuously for 1.5 km to the northwest and 

for 11.5 km to the southeast (fig. 2), the principal 

occurrence of wagnerite is within the area shown in figure 

3. Wagnerite has also been identified as a trace constituent 

of rutile-bearing biotite-quartz-plagioclase gneiss in the 

area between Beaver Brook and North Beaver Brook (fig. 

2).

The wagnerite-bearing sillimanite-plagioclase gneiss is 

white or light gray, fine to coarse grained, poorly foliated, 

and texturally complex. Aggregates of prismatic sillimanite, as much as 12 cm long and 1 cm thick, and grains 

of corundum, as long as 2.3 cm, are diversely oriented in a 

fine- to medium-grained matrix rich in plagioclase and
WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

105° 28'10"

EXPLANATION

Quaternary colluvium

Pegmatite

Quartzo-feldspathic gneiss

Hornblende gneiss

Light-colored gneisses 

s, wagnerite-bearing sillimaniteplagioclase gneiss 

b, biotite-quartz-plagioclase gneiss

Contact Approximately located; dashed 

where inferred or gradational; short 

dashed where concealed

Strike and dip of compositional layering 

and foliation

15 20

J_____|_

CONTOUR INTERVAL 5 FEET 

DATUM IS APPROXIMATE MEAN SEA LEVEL

FIGURE 3. Geologic map of wagnerite locality, Santa Fe Mountain. Geology and topography by D. M. Sheridan and S. P. Marsh.

fibrolitic sillimanite. Wagnerite is recognizable in hand 

specimens and outcrops as aggregates of small yellow to 

yellowish-tan grains that commonly are complexly intergrown with other minerals of the rock. Such aggregates are 

generally small, mostly 2 to 5 mm across. Smaller individual grains of wagnerite are also common but are 

recognized readily only in thin section. Other constituents 

of the gneiss are biotite, rutile, apatite, monazite, zircon, 

tourmaline, muscovite, and, locally, chlorite. Foliation in 

the sillimanite-plagioclase gneiss is in general obscure in 

the outcrops, owning to the diversely oriented large grains 

of corundum and aggregates of prismatic sillimanite. In 

some thin sections, however, foliation is well shown and is 

defined by aggregates of fibrolitic sillimanite, elongate 

grains of plagioclase, and oriented flakes of biotite.

Modes of the light-colored gneisses of the wagnerite 

locality were determined by the point-count method (1,000 

points each) and are reported in table 1. Modes 1-7

represent wagnerite-rich rocks in which plagioclase and 

sillimanite are the principal constituents. Modes 8 and 9 

represent wagnerite-bearing rock with more biotite than 

sillimanite. Because rock specimens for these thin sections 

were selected preferentially to study the wagnerite, the 

modes do not represent normal mineralogic percentages. 

We estimate that wagnerite and corundum each form 

about 1 percent of the average rock and that rutile makes 

up 1-2 percent. In the sillimanite-plagioclase gneiss, 

quartz is present only in trace amounts as tiny rounded 

inclusions in other minerals.

The biotite-quartz-plagioclase gneiss, the associated 

hornblende gneiss, and the quartzo-feldspathic gneiss (fig. 

3) are fine to medium grained moderately well foliated 

rocks. Some parts of the hornblende gneiss and the lightcolored biotite-quartz-plagioclase gneiss show welldeveloped compositional layering on a scale of a few centimetres, but other parts contain massive layers 1 m thick.
DESCRIPTIVE MINERALOGY

TABLE 1. Modes (volume percent) of light-colored gneisses, Santa Fe Mountain wagnerite locality,

Colorado

Wagnerite-bearing sillimanite-plagioclase gneiss

Modes. .................... ..

Quartz..............

Plagioclase ...... 

Microcline .......

Sillimanite....... 

Biotite..............

Muscovite 

(and Sericite) 

Wagnerite. .......

Apatite.............

Rutile. .............

Corundum.......

i 

11-4X2

Trace

74.4

12.8 

1 5

4.8

.7

3

4.8

2 

1 1 6X

47.3

45.0

1.8 

9

3

4.7

3 

21A

71.6

19.8 

.1

2.0 

4.6

3

.9

.7

4 

24AX

64.7

25.7

.8 

68

.6

1.2

5 

11-8X2

45.7

38.9 

.3

3.7 

6 9

2.1

.1 

2.2

6

S3X

52.4

35.5

1.0

76

?.4

.8 

.3

7 

23A1

53.0

28.5 

.3

4.5 

109

1.2

1.0

8 

11-2X

74.6

2.2 

14.0

3.3 

L4

.5

3.1 

.5

9 

11 -3X

Trace

68.8

3.3 

10.2

10.1 

.3

.2

3.1 

1.5

Biotite-quartz-plagioclase 

gneiss

10

7A

29.3 

56.3 

.2

'12.5 

1.0

.1

11

9A

38.8 

50.5

4.6

4.4

.5

12 

9D

36.0 

46.7

2.0 

10.8

3.3

.2

Monazite and

(or) zircon.... .2 Trace Trace Trace .1 Trace .3 .4 .2 Trace Trace Trace

Tourmaline..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .1 ......

Chlorite........... .5 ...... Trace .2 Trace Trace .3 ...... 2.3 .6 1.1 1.0

Total..... 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Modes 10-12 of biotite-quartz-plagioclase gneiss (table 

1) indicate that the principal constituents, in order of 

increasing abundance, are biotite, quartz, and plagioclase. Rutile (no more than 0.5 percent) is less abundant 

than in the wagnerite-bearing rock. Wagnerite was not 

observed in samples of the biotite-quartz-plagioclase 

gneiss from the Santa Fe Mountain locality.

DESCRIPTIVE MINERALOGY

METHODS USED FOR OPTICAL 

DETERMINATIONS

Except for optic angles, all optical data for wagnerite 

and other minerals from Santa Fe Mountain (tables 2, 4) 

were obtained on single grains that were selected from 

mineral separates and that were studied petrographically 

by the spindle-stage procedures described by Wilcox 

(1959). Most of the determinations of refractive indices 

were made by use of the focal masking techniques 

described in detail by Cherkasov (1955a, b; 1957). A few 

determinations of refractive indices were made by the 

Becke line method; an interference filter was used that 

passes a wavelength near the D-line of the spectrum. All 

except one of the optic angles reported in table 2 were 

determined from thin sections mounted in a universal 

stage. The exception was determined on the spindle stage 

using Mallard's method for a centered acute bisectrix 

figure.

The refractive indices of 3 grains of wagnerite from 

Bamle, Norway (U.S. Natl. Mus. spec. C4151), reported in 

table 3, were determined by spindle state procedures and 

focal masking techniques. Our measurement of the optic 

angle of each of these grains was facilitated by I. J. 

Witkind, who carefully mounted each grain so that its

optic plane was normal to the spindle axis. The measurement of the optic angle was then made directly by simple 

rotation of the spindle from one melatope to the other.

WAGNERITE

The wagnerite from Colorado is anhedral, mostly fine 

grained but ranging to medium grained, and pale yellow 

to yellowish tan. The luster is vitreous to slightly resinous. 

Cleavage (100) is very poor and other cleavage was not 

observed. The specific gravity, determined by Fahey's 

method (Fahey, 1961) on the material ground for chemical 

analysis, is 3.13. In transmitted light the wagnerite in thin 

section is colorless; large grains in immersion mounts are 

faintly yellowish and nonpleochroic. The mineral is 

biaxial positive. The indices of refraction and 2V (table 2) 

show a range in values: a =1.565-1.571, /? =1.567-1.572, 

y =1.578-1.585 (all ±0.002); (+)2F=28°-33° (±1°). Slight

TABLE 2. Optical data for wagnerite from Santa Fe Mountain,

Colorado

Sample 

No. SF11-7 .. ........

21..............

24, No. 1... 

2S-A1 ........

21A ...........

24, No. 3... 

24, No. 2...

Indices of refraction (±0.002)"

a

.565 

.566 

.566 

.568 

.569 

.569 

.571

/?

1.567 1.568

.567 

.568 

.570 

.571 

.570 

.572

y

1.578-1.579 

1.580 

1.581 

1.582 

1.583 

1.583 

1.585

Sample 

No. SF24AX..

23A1...

11-2....

11-7....

11-4....

21B.....

21A.....

24B.....

23B2X

Optic angle (measured)

(+)2F

....... 228°±0.5°

....... S28.5°*1.0°

....... 229°±1.0°

...... 2430°-31°±1.0°

....... 231°±1.0°

....... 231°±0.5°

....... 231.5°±1.0°

....... 232.5°±1.0°

....... 233°±0.5°

"Determined by spindle stage techniques.

determined from thin sections on universal stage.

'Determined on spindle stage from centered acute bisectrix figure by Mallard's method.

'Zoned.
WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

variation of optical properties occurs within many 

individual grains, a variation limited to 1° or less in 2V 

and to correspondingly small changes in indices. The birefringence ( 7 - a ), calculated from refractive index determinations, ranges from 0.013 to 0.015. Dispersion isr > v, 

weak. The extinction angle (ZAc) was measured at 

approximately 23° by universal stage techniques in one 

thin section, but the (100) cleavage is so poorly developed 

that a representative value for ZAc cannot be reported. 

The. optical data for wagnerite from Santa Fe Mountain 

are compared with optical data for wagnerite from several 

other localities in table 3.

As viewed in thin section, individual grains of 

wagnerite range in size from 0.02 to 6.1 mm. Most individual grains are in the size range 0.2-0.6 mm. Aggregates of 

wagnerite grains, complexly intergrown with plagioclase 

and other minerals of the rock, are also common, ranging 

in size from 1 mm to 12 mm but most commonly in the size 

range 2-5 mm. One elongate aggregate observed in hand 

specimen is 20 mm long but is so complexly intergrown 

with other minerals that no more than 50 percent of the 

aggregate is wagnerite.

TABLE 3. Comparison of optical data for wagnerite

'Calculated from published 2£ as given in sources of data (c) and (d).

Sources of data:

(a) This report (table 2).

(b) This report. The indices reported here are the range in values 

obtained by spindle-stage techniques on 3 grains of wagnerite, 

U.S. Natl. Mus. spec. C4151 from Bamle, Norway. Measurement of 2FZ was done by orienting the optic plane of each grain 

normal to the spindle axis; in this manner, measurement of the 

optic angle was made directly by rotation of the spindle from 

one melatope to the other.

(c) Indices of refraction from Michel-LeVy and Lacroix (1888, p. 290). 

The 2V was calculated from 2E=59° 30', reported by Doelter (1918, 

p. 319).

(d) Indices of refraction from Hegemann and Steinmetz (1927, p. 55). 

The 2V was calculated from 2E=45° 22^', reported by Hegemann 

and Steinmerz (1927, p. 55).

(e) Finko (1962, p. 1425).

(f) StaneTc (1965, p. 67).

The wagnerite appears to be entirely anhedral; no 

crystal faces were observed despite the study of numerous 

thin sections. Most commonly the individual grains are 

elliptical to very irregular or ameboid (fig. 4) in shape. The 

larger grains tend to be blocky to rounded and have very 

irregular boundaries (fig. 5). Some of these grains contain 

myriads of small inclusions of rutile; others poikiloblastically enclose small grains of plagioclase, sillimanite, monazite, and other minerals.

Some groups of closely spaced wagnerite grains seem to 

be composed of distinct individuals that are separated by 

plagioclase and other minerals of the rock. When viewed 

through crossed polars, however, most of the wagnerite 

grains in such groups have identical interference color and 

come to extinction at the same position. Very likely such 

wagnerite grains are connected in the third dimension and 

represent a type of branching skeletal growth, which, in 

the plane of the thin section, shows up mainly as a 

complex intergrowth approaching that of a poikiloblastic texture (fig. 6).

In addition to poikiloblastic inclusions of grains of 

other minerals of a size large enough to be readily identiLocality

Santa Fe

Mountain,

Colo. .......

Bamle,

Norway...

Do........

Werfen,

Austria ....

Kyakhta,

U.S.S.R. ..

Dolni

Bory,

western

Moravia,

Czechoslovakia...

Source of 

data

(a)

(b)

(c)

(d)

(e)

<f)

Indices of refraction

a

1.565-1.571

±0.002

1.569-1.571

±0.002

1.569

1.5678

1.577

±0.001

1.568

£

1.567-1.572

±0.002

1.570-1.572

±0.002

1.570

1.5719

1.582

±0.001

1.571

y

1.578-1.585

±0.002

1.582-1.584

±0.002

1.582

1.5824

1.595

±0.001

1.582

(+)2F

28°-33°

±1°

37°-38^°

±1°

!36° 50'

128° 24'

32°

±1°

Small.

FIGURE 4. Large grain of wagnerite (\AO occupying central part of 

photomicrograph is ameboid in shape; smaller grains of wagnerite 

are elliptical to irregular. Other minerals are plagioclase (P), monazite (M), apatite (A), fibrolitic sillimanite (fs), and muscovite (ms). 

Crossed polars.
DESCRIPTIVE MINERALOGY

FIGURE 5. Large blocky grain of wagnerite (W) poikiloblastically 

encloses rows of grains of rutile (R). Apatite (A) forms a thin rim 

along the boundary of the wagnerite grain. Other minerals are 

plagioclase (P), biotite (B), fibrolitic sillimanite (fs), and prismatic 

sillimanite(S). Crossed polars.

fiable in thin section, many of the medium to large grains 

of wagnerite show cloudy areas crowded with abundant 

very tiny inclusions. At low to moderate magnification in 

plane-polarized light, these cloudy areas are bluish. 

Commonly, the cloudy areas are located at or near the 

center of the wagnerite grains, and the surrounding 

borders of wagnerite are relatively clear of inclusions; in 

other wagnerite grains, the cloudy areas are located 

asymmetrically near the edge of the grains (fig. 9). A 

photomicrograph (fig. 7), taken at high magnification 

with upper and lower polars removed, shows part of a 

wagnerite grain clouded with tiny inclusions. Toward the 

center of the clouded area, the inclusions are principally 

equidimensional with rounded form, and they commonly 

range in size from 0.0005 to 0.01 mm. Toward the edge of 

the clouded area, elongate prismatic inclusions, as long a 

0.1 mm, are more abundant and are alined in a rectilinear 

pattern. Identification of these tiny inclusions proved 

impossible by ordinary petrographic methods in thin 

section, but an attempt was made to learn their 

mineralogic nature by other methods. During the

FIGURE 6. Complex intergrowth of closely spaced grains of wagnerite 

(W) and plagioclase (P). However, as most of the wagnerite grains 

shown here have the same interference color and come to extinction 

at the same position, they are probably interconnected in the third 

dimension and comprise a complex branching skeletal or poikiloblastic growth. Other minerals are rutile (R), monazite (M), apatite 

(A), and muscovite(ms). Crossed polars.

chemical analysis of wagnerite, the analytical procedure 

involved digestion of part of the sample in nitric acid. The 

insoluble residue from this digestion was studied carefully by Mrose through X-ray techniques. This .residue, 

which represents at least part of the inclusions, was found 

to be sillimanite, rutile, and quartz, plus minor mica and 

xenotime. If apatite or any other mineral soluble in nitric 

acid were present as part of the suite of tiny inclusions in 

the wagnerite, it probably was dissolved during the 

analytical procedure.

Although many of the wagnerite grains are in direct 

contact with the other minerals of the rock, many others 

show a partial to complete enveloping film of apatite (fig 

8). Each rim is formed of a single optically continuous 

apatite crystal. The thickness of the rim ranges from less 

than 0.01 mm to 0.2 mm but most commonly is about 0.02 

mm. Although the rims of apatite are perhaps most 

commonly present between wagnerite arid plagioclase or 

fibrolitic sillimanite, they have also been observed 

between wagnerite and other minerals of the rock, such as 

biotite, monazite, rutile, muscovite, and chlorite. Where
WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

« *f*i4^ -H»-I *rf. y<=? '*

/

 >j

FIGURE 7. Part of a large wagnerite grain that is crowded with tiny 

inclusions. Bottom of photomicrograph is toward the interior of 

wagnerite grain and shows abundant equidimensional to rounded 

inclusions. Top of photomicrograph is near edge of wagnerite grain 

and is relatively free of inclusions. Between the clear edge and the 

densely clouded interior, elongate prismatic inclusions are alined 

in rectilinear fashion. Inclusions are chiefly sillimanite, rutile, and 

quartz. Photomicrograph taken with upper and lower polars removed.

two or more wagnerite grains are closely spaced in the 

rock, the apatite rims commonly coalesce over part of their 

extent, forming the thicker observed portions of such rims. 

Some of the larger wagnerite grains not only have an 

external rim of apatite but also have internal rims of 

apatite bordering poikiloblastic inclusions of small grains 

of plagioclase and other minerals of the rock. Although 

commonly composed of clear apatite, in one instance the 

apatite rim has formed around a wagnerite grain 

containing an asymmetrically located area clouded with 

tiny inclusions (fig. 9); where the cloudy area extends to 

the edge of the wagnerite grain, the apatite rim is also 

crowded with abundant tiny inclusions.

In some thin sections the wagnerite has been partly 

altered to an unidentified fine-grained material which 

appears brownish in plane-polarized light and which has 

no conspicuous identifiable characteristics when viewed 

with crossed polars or when examined by conoscopic 

study.

FIGURE 8. Apatite (A) forms rims on wagnerite (W). Wagnerite grain 

at top center has only a partial rim of apatite, but all other wagnerite grains shown here are completely rimmed by apatite. Rims on 

several grains at top center and upper right coalesce and surround 

a small grain of plagioclase (P). Other minerals are fibrolitic sillimanite (fs) and prismatic sillimanite (S). Crossed polars.

OTHER MINERALS

The optical characteristics of the associated minerals 

from the Santa Fe Mountain wagnerite-bearing rocks were 

also studied. These properties together with those of some 

of the minerals of the associated rocks are reported in table 

4.

Plagioclase. The plagioclase of the wagnerite-bearing 

sillimanite-plagioclase gneiss is albite (An6-An8 ), as 

determined in two samples (SF-21 and SF-24A, table 4). 

Commonly showing well-developed albite twinning (figs. 

6, 12), the plagioclase grains are elongate parallel to the 

foliation; they range in length from 0.04 to 7 mm but most 

commonly are about 1.2 mm. The plagioclase in biotitequartz-plagioclase gneiss (SF-7A, table 4) is also albite 

(An6) and occurs as grains averaging about 0.6 mm in 

length. The plagioclase of these light-colored gneisses is 

more sodic than the plagioclase of the darker colored metamorphic rocks in this area. Plagioclase in the hornblende 

gneiss (SF-20B, table 4) is andesine (An31 ), and plagioclase in the quartzo-feldspathic gneiss is oligoclase (An27).
DESCRIPTIVE MINERALOGY

FIGURE 9. Large grain of wagnerite (W) occupies upper two-thirds 

of photomicrograph and is rimmed by apatite (A), which completely 

encloses two smaller grains of wagnerite at left. Where the edge 

of large wagnerite grain is clear and relatively free from tiny inclusions, as at left center, the adjoining apatite rim is also clear. Where 

edge of large wagnerite grain is clouded with tiny inclusions, as 

at right, the adjoining apatite rim is also clouded with inclusions. 

Other minerals are plagioclase (P), rutile (R), and chlorite (ch). 

Polars partly crossed.

Biotite. Most of the biotite in the sillimaniteplagioclase gneiss and the biotite-quartz-plagioclase 

gneiss is very pale brown, as viewed under the hand lens 

and in thin section. It resembles the biotite found in the 

cordierite-bearing biotite gneisses of the east-central Front 

Range (Gable and Sims, 1969, p. 39) rather than the darkbrown to black biotite of the more common gneisses. 

Optical data for pale-brown biotite from two samples of 

sillimanite-plagioclase gneiss (SF-21; SF-11-3) and from 

one sample of biotite-quartz-plagioclase gneiss (SF-7A) 

are reported in table 4. All three samples of biotite are 

biaxial negative (2V estimated no more than 10°). 

Comparison of the ft index (ranging from 1.584 to 1.595) 

with Winchells' graph (Winchell and Winchell, 1951, p. 

374) suggests that this is a low-iron, high-magnesium 

variety; thus the biotite is probably close to the 

phlogopite-eastonite part of the compositional field. 

Biotite flakes range in size from 0.02 to 2.6 mm but average 

about 0.5 mm in both of the light-colored gneisses.

Sillimanite. Sillimanite in the sillimanite-plagioclase 

gneiss occurs in two varieties. Fibrolitic sillimanite occurs 

in elongate to elliptical aggregates of tiny needles oriented 

parallel to the foliation (figs. 11, 12) and other mineral 

lineations; most aggregates are 0.5-10 mm long, although 

locally some are as long as 19 mm. Coarse prismatic sillimanite crystals are diversely oriented in the rock, 

commonly cutting other minerals (figs. 13, 14). Single

prismatic sillimanite crystals generally are 0.1-0.2 mm 

thick and 1.5-2 mm long; aggregates of these crystals are 

locally as much as 12 cm long and 1 cm in diameter. 

Refractive indices of prismatic sillimanite from two 

samples (SF-21 and SF-24A, table 4) are at the lower end of 

the range of values reported by Deer, Howie, andZussman 

(1962, p. 121).

Monazite. Monazite occurs as small, clear, paleyellowish grains. These grains range in size from 0.01 to 

0.2 mm and are commonly associated with rutile and 

wagnerite. Refractive indices a and (3, determined for 

sample SF-11-3 (table 4), are in the lower range of values 

commonly reported.

Apatite. Two forms of apatite occur in the sillimaniteplagioclase gneiss: (1) individual grains that are rounded 

to blocky and locally prismatic, clear and colorless to 

dusky, and about the same average size and distribution as 

those of wagnerite; (2) partial to complete rims on 

wagnerite (noted in the description of wagnerite and 

shown in figs. 5, 8, 9). The apatite that occurs as individual grains ranges in size from 0.02 to 1 mm; aggregates are 

as much as 6.4 mm across. Locally, prismatic grains of 

apatite occur as inclusions in wagnerite (fig. 10). The 

refractive indices determined for individual grains of 

apatite from two samples (SF-11 and SF-21, table 4) 

suggest that it is fluorapatite.

Corundum. Corundum, ranging in color from pink to 

grayish, occurs in the sillimanite-plagioclase gneiss in 

grains ranging in size from 0.04 mm to 2.3 cm. Many of the 

larger grains are subhedral to euhedral and show wellFIGURE 10. Apatite (A) occurs as prismatic to blocky grains included 

in wagnerite (W). Other apatite grains are included in plagioclase 

(P). The wagnerite grain at upper right also has a thin partial rim 

of apatite. Other minerals are monazite (M), fibrolitic sillimanite 

(fs),and prismatic sillimanite (S). Crossed polars.
10 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

TABLE 4. Optical data for other minerals from wagnerite locality, Santa Fe Mountain, Colorado

Biaxial minerals

Sample Indices of refraction1 Optic 

Mineral Rock type Mr. «on u ,!,.

SF- a p 7

Plagioclase.

Do. 

Do.

Do. 

Biotite..

Do. 

Do.

Sillimanite.

Do.......

Andalusite.

Monazite....

Sillimanite-plagioclase gneiss containing wagnerite, rutile, and 

corundum.

...do.........................................

Rutile-bearing biotite-quartzplagioclase gneiss.

Hornblende gneiss............................

Sillimanite-plagioclase gneiss containing wagnerite, rutile, and 

corundum.

...do.........................................

Rutile-bearing biotite-quartzplagioclase gneiss.

Sillimanite-plagioclase gneiss 

containing wagnerite, rutile, and 

corundum.

...do.........................................

Feldspathic layer in rutile-bearing 

biotite-quartz-plagioclase gneiss.

Sillimanite-plagioclase gneiss 

containing wagnerite, rutile, and 

corundum.

21 1.532 1.536 1.541 (+) Composition: 2albite (An6).

24A 1.533 1.537 1.542

7A 1.532 1.536 1.541

20B 1.544 1.548 1.552

21 1.557 1.595 1.595

11-3 1.548 1.584 1.584 

7A 1.549 1.585 1.585

Composition: 2albite (Ang ). 

Composition: 2albite (An6).

Composition: 2andesine (An31 ). 

Pleochroism:

a ^colorless to very pale yellowish tan; 

B= y~ pale brown. 

Do. 

Do.

21 1.656 1.658 1.676 (+) Prismatic variety.

24A 1.654 1.657 1.674 (+) 

4F 1.628 1.634 1.639 (-)

11-3 1.787 1.788 (3 ) (+) 

±0.003 ±0.003

Do. 

Pleochroism: a= pink; J3= 7 = colorless.

Absorption: J3 > <* = 7-

Uniaxial minerals

Rock type

Sample Indices of refraction1 Optic

No. _____________ sign

SF- E <i)

Remarks

Apatite................... Sillimanite-plagioclase gneiss containing wagnerite, rutile, and 

corundum. 

Do................... ...do.........................................

Corundum............. ...do.........................................

Tourmaline. ,.do.

11 1.629 1.632

21 1.631 1.635

15 1.759 1.767

±0.003 ±0.003

11-3 1.615 1.638

Do................... Feldspathic layer in rutile-bearing 4F-1 1.613 1.635

biotite-quartz-plagioclase gneiss.

Do. .do. 4F-2 1-612 1.635

Pink in hand specimen.

Dichroism:

e= colorless to very pale tan;

c>= yellowish brown. 

Dichroism:

e= colorless to very pale blue;

<a= greenish blue. 

Dichroism:

c= very pale blue;

<a= variegated greenish blue to brownish yellow.

 Precision of refractive index determinations is ±0.002 except where indicated. Determined by spindle stage procedures. 

'Plagioclase composition determined from curves for low-temperature plagioclase by Smith (1960, pi. 12). 

'Not determined.

developed pseudohexagonal parting; thin sections of such 

grains commonly show twinning. Many of the smaller 

grains of corundum are anhedral to angular kernels, many 

of which resemble graphic shapes. Such small kernels of 

corundum, 0.06-1 mm across, occur as closely spaced 

individuals that comprise aggregates 3 mm across in 

fibrolitic sillimanite clots. Individual grains of corundum 

within an aggregate commonly have the same interference color and come to extinction at the same position 

upon rotation of the microscope stage, suggesting that they 

are connected elements of a single skeletal crystal. 

Refractive indices for corundum from one sample (SF-15) 

are reported in table 4.

Andalusite. Andalusite has been recognized only in a 

single thin feldspathic layer within the biotite-quartzplagioclase gneiss. It occurs as blocky pinkish-white 

grains ranging in size from 0.2 to 1 mm, and it is associated 

with plagioclase, quartz, muscovite, and chlorite. Optical 

data for andalusite from one sample (SF-4F) are reported 

in table 4.

Tourmaline. Tourmaline occurs sparsely in both the 

sillimanite-plagioclase gneiss and the biotite-quartzplagioclase gneiss. It is fairly common as small yellowishbrown to pale-greenish-blue grains in heavy mineral 

separates prepared from rock samples; although a few 

grains were observed in thin sections, none was seen in
MINERAL ASSEMBLAGES AND TEXTURAL RELATIONS 11

contact with wagnerite. In a sillimanitic biotite-quartzplagioclase gneiss that occurs along the trace of the lightcolored gneiss unit about 100 m northwest of the wagnerite locality, sparse small aggregates of tourmaline, as 

much as 2 cm across, are poikiloblastically intergrown 

with other minerals of the rock; individual brownish crystals are 2-6 mm long and 0.5 mm in diameter. Optical data 

for tourmaline from rocks of the mapped area (fig. 3) are 

reported in table 4. The refractive indices suggest that the 

tourmaline is dravite.

Other minerals from the wagnerite locality. Quartz 

occurs only in trace amounts in the silimanite-plagioclase 

gneiss, where it is present as small rounded inclusions in 

other minerals of the rock. In the biotite-quartzplagioclase gneiss, however, quartz is a major constituent 

occurring as grains ranging from 0.04 to 3.8 mm in size 

and averaging about 0.5 mm. Rutile is a characteristic 

minor constituent of both the light-colored gneisses of the 

Santa Fe Mountain locality. Commonly splendent red in 

color, it ranges from yellow to nearly black. Heavy mineral 

separates indicate that the average rutile content of the 

sillimanite-plagioclase gneiss is between 1 and 2 percent. 

The average rutile content of the biotite-quartzplagioclase gneiss is no more than 0.5 percent. Rutile 

grains range in size from 0.01 to 0.6 mm, but most are in 

the range of 0.06-0.1 mm. Although most of the rutile 

grains are anhedral, some are subhedral to euhedral. 

Zircon, although identified optically in grains picked 

from heavy mineral separates, does not appear to be as 

abundant in the sillimanite-plagioclase gneiss as 

monazite. Xenotime was identified only in the insoluble 

residue from the chemical analysis of wagnerite. White 

mica occurs in both the sillimanite-plagioclase gneiss and 

the biotite-quartz-plagioclase gneiss. All samples of white 

mica studied by X-ray proved to be muscovite. Many 

grains of the muscovite are about the same size as biotite 

(about 0.5 mm). Sericite (finely crystalline muscovite) is 

found in plagioclase and along the boundaries of some of 

the sillimanite aggregates. Chlorite is fairly common as a 

minor constituent of both of the light-colored gneisses 

where it apparently formed as an alteration or pseudomorph of biotite. The chlorite seems to have a birefringence of about 0.010 and is colorless in thin section. 

Universal-stage study of the chlorite in one thin section 

(SF-11-3X) of wagnerite-bearing rock indicates that (+) 2V 

of the mineral is about 13°.

MINERAL ASSEMBLAGES AND 

TEXTURAL RELATIONS

During petrographic studies of wagnerite-bearing 

gneiss, special attention was focused on mineral 

assemblages and on textures, structures, and intergranular relations. Although one or more of the minerals 

listed in the following assemblage may be missing from a

particular specimen, textural relations indicate that a 

single stable-state assemblage characterizes this rock: 

wagnerite + plagioclase (albite) + fibrolitic sillimanite + 

magnesian biotite. To this assemblage may be added small 

amounts of rutile, monazite, zircon, and apatite, minerals 

inferred to represent phases belonging to an early stage of 

crystallization during the high-grade regional metamorphism. Rock textures indicate that corundum, 

prismatic sillimanite, and some of the apatite (the form 

that occurs as rims on wagnerite) crystallized later, but 

very likely during the same regional metamorphism.

Fibrolitic sillimanite, plagioclase, biotite, and 

wagnerite define the foliation of the sillimaniteplagioclase gneiss. Commonly elongate aggregates of 

fibrolitic sillimanite alined in foliation surfaces also form 

a linear structure. Elongate grains of plagioclase and 

wagnerite, flattened in the foliation plane, are intergrown 

to varying degrees. Small grains and grain clusters of 

wagnerite concentrated at boundaries between other 

minerals (fig. 11) are strongly oriented in the plane of 

foliation. Similarly, wagnerite grains enclosed within

FIGURE 11. Foliation in sillimanite-plagioclase gneiss is defined by 

fibrolitic sillimanite (fs). Grains of wagnerite (W) that are concentrated along grain boundaries of other minerals are also strongly 

oriented in the plane of the foliation. Other minerals are plagioclase(P), prismatic sillimanite (S), and monazite (M). Crossed polars.
12 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

FIGURE 12. Foliation in sillimanite-plagioclase gneiss is defined by fibrolitic sillimanite (fs). Grains of wagnerite (W) that are enclosed 

within grains of plagioclase (P) are also strongly oriented in the plane of the foliation. A single optical orientation is shared by numerous 

grains of wagnerite. Other minerals are monazite (M) and prismatic sillimanite (S). Crossed polars.

single grains of plagioclase commonly are also strongly 

oriented (fig. 12). In part, such groups of wagnerite grains 

are complexly intergrown skeletal growths; a single 

optical orientation is commonly shared by dozens of 

separate but closely spaced grains. (See figs. 6, 12.) Such 

common orientation may be confined within a single 

plagioclase grain or may cross host-crystal boundaries, or 

a single plagioclase grain may enclose several differently 

oriented skeletal wagnerite growths. Some of the larger 

wagnerite grains enclose rows of rutile grains (fig. 5) or 

may surround other minerals that define the foliate fabric. 

In contrast, prismatic sillimanite and corundum in 

coarse grains disrupt the foliate fabric of the wagneritebearing gneiss. Prismatic sillimanite typically cuts plagioclase, wagnerite, and fibrolitic sillimanite (figs. 13, 14). It 

cuts across the foliation and fails to parallel the lineation 

of the fibrolitic sillimanite. Corundum grains similarly 

interrupt the foliation. Small anhedral corundum grains, 

groups of small grains in optical continuity, skeletal 

crystals enclosing other minerals, and large subhedral to 

euhedral crystals of corundum seem to represent varying 

stages of crystallization. Characteristically, these

FIGURE 13. Prismatic sillimanite (S) cuts wagnerite (W) and plagioclase (P). Other grains are fibrolitic sillimanite (fs). Crossed polars.
MINERAL ASSEMBLAGES AND TEXTURAL RELATIONS 13

FIGURE 14. Prismatic sillimanite (S) cuts wagnerite (W), plagioclase 

(P), and fibrolitic sillimanite (fs). Crossed polars.

FIGURE 15. Corundum (C) contains numerous tiny needles of sillimanite that are oriented parallel to the alinement of fibrolitic sillimanite (fs) in sillimanite-plagioclase gneiss. A small grain of 

plagioclase (P) is partly enclosed by corundum. Plane-polarized light.

*M ^w.y^--*-? :J^.-'w^*N&A" .A",.ftw* ;;~> ? ask?, A,

FIGURE 16. Grain of wagnerite (W) at top center is partly surrounded 

by a border of corundum (C). Numerous grains of rutile (R) occur 

along the grain boundaries of wagnerite in this specimen. Other 

minerals are plagioclase (P), biotite (B), monazite (M), and prismatic 

sillimanite (S). Plane-polarized light.

corundum grains are developed in aggregates of fibrolitic 

sillimanite and contain remnants of sillimanite needles 

that still retain the linear orientation of the fibrolitic 

aggregates (fig. 15). Rarely, wagnerite is surrounded in 

part by a corundum border (fig. 16).

Apatite and wagnerite have several textural relationships. Locally, prisms of apatite are surrounded by 

wagnerite (fig. 10); some aggregates of apatite grains are 

surrounded by a border of elongate wagnerite grains; a 

considerable proportion of the wagnerite grains are 

partially or completely rimmed by apatite. (See figs. 5, 8, 

9.) Rims of apatite occur not only on exterior surfaces of 

wagnerite but also between the wagnerite and its poikiloblastic inclusions. Apatite rims have been observed 

between wagnerite and the following minerals: plagioclase, fibrolitic sillimanite, biotite, monazite, rutile, 

muscovite, and chlorite. The rims, therefore, do not appear to be a simple reaction rim of the type that occurs only 

between a specific pair of minerals.
14 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

TABLE 5. Chemical analyses of wagnerite

[Leaders (...) indicate not determined]

This report 

(Analyst, Laura Reichen)

Color..................................

MgO. ........................

FeO..........................

MnO.................. .......

FejQs ........................

CaO..........................

Pz05 .........................

F ..................... .... ..

Cl..............................

H2O+ . .......................

HzO~.... ....... .............

A1203 ........................

TiO2 . ................. .......

SiO2 . .........................

Subtotal.........

LessF = O...............

Less Cl = O..............

Santa Fe Mountain,

Colo.

Pale yellow

Theoretical Determined 

(percent) (percent)

49 59 45 97

1 64

0.47

1.36

43 65 41 84

11.68 «10.3

0.46

0.00

0.00

1.05

044

5 1 84

104.92 105.37

4 92 4 33

0.10

Recalculated1 Ratios

48.31)

1.72} 2.03 

0.49J

42.89 1.66 

10.72) 

1 0.96 

0.48 j

0=4.06

104.61 

4.51 

0.10

Hegemann and 

Steinmetz (1927)

Werfen, Austria

Pale yellow

Determined2 Ratios 

(percent)

48.35) 

0.95 } 2.00 

0.70 )

43.45 i.OO 

11.49 0.99

0=4.60

104.94 

4.84

Finko (1962)

Kyakhta, Buryat, U.S.S.R.

Pale yellow

Determined 

(percent)

40.42) 

9.90 \ 

2.00)

4L60 

11.08

tr.

105.00 

4.65

Ratios Determined 

(percent)

42.63 

1.99 4.88 

0.45 

4.17

i'.OO 4L36 

0.99 10.00

...... 6.65 

O=4.00

104.14 

4.19

Orange

Reclaculated3

42.84) 

8.67 1 

0.45)

4L56 

10.05^

6.65'J

104.22 

4.22

Ratios

2.01

i.66

0.96 

O=4.0!

Total.

Formula......

100.00

Mgj(P04)F

100.94 100.00 100.10 100.35 99.95 100.00

(Mg,Fe,Mn) *. , PO4(F,Cl)o.w 

Mg:Fe:Mn=0.97:0.02:0.01

(Mg,Fe,Mn) 2.0o PO4F«.M (Mg,Fe,Mn),.M PO«Fo.»t 

Mg:Fe:Mn=0.98:0.01:0.01 Mg:Fe:Mn=0.86:0.12:0.02

(Mg,Fe,Mn) 2.01 PO«(F,OH)o.9« 

Mg:Fe:Mn=0.89:0.10:0.01

'Recalculated to 100 after deducting CaO as fluorapatite, AljOj, TiOz, and SiO». 

'Calculated to oxide values by the authors of this report from the original analysis. 

'Recalculated to 100 by the authors of this report after first converting FejOj to FeO.

 Determined by specific ion electrode method by Johnnie Gardner, U.S. Geological Survey. 

5Acid soluble SiOj.

From the textural and mineralogic relations we make 

the following interpretations. The foliate fabric defined by 

wagnerite, plagioclase, fibrolitic sillimanite, and biotite 

apparently formed early during high-grade regional 

metamorphism. Except for prismatic sillimanite, 

corundum, some apatite, and minor chlorite and 

muscovite, the minerals of the sillimanite-plagiodase 

gneiss apparently crystallized at about the same time. 

Development of corundum and the large diversely 

oriented aggregates of prismatic sillimanite occurred later 

but probably during the same high-grade regional metamorphism. The larger grains of wagnerite may also 

belong to this later stage of crystallization. Chlorite and 

sericite probably formed still later under lower grade metamorphic conditions.

CHEMISTRY

Sample preparation for chemical analysis. Because 

wagnerite occurs at the Santa Fe Mountain locality as a 

minor constituent of rutile-bearing gneiss, 1,000-1,500 g 

of the gneiss that showed the greatest visible concentrations of wagnerite was used to prepare a sample large 

enough for chemical analysis. The sample of gneiss was 

broken into M-in. (6 mm) pieces, then it was ground to 

approximately 65 mesh (0.208 mm); the ground material 

was repeatedly washed with water and the fines decanted. 

After air drying, this material was sieved and the portion 

between 0.208 mm and 0.104 mm was retained; this 

fraction was then separated into light and heavy fractions, 

by use of bromoform (sp. gr., 2.86). The heavy fraction 

( > 2.86), which contained wagnerite, rutile, corundum, 

mica, sillimanite, and fluorapatite, was put through a 

Frantz isodynamic magnetic separator; splits were taken at 

0.3 amps, 0.5 amps, and 1.3 amps. Wagnerite was concentrated in the 0.5 amp fraction. Compound grains 

(wagnerite-rutile, wagnerite-sillimanite, wagneriteflourapatite, and silimanite-rutile) were removed by handpicking under the binocular microscope. Four and onehalf grams of visibly pure wagnerite were obtained for 

chemical analysis.

Methods of analysis. The complete chemical analysis 

of wagnerite from Santa Fe Mountain, Colo. is given in 

table 5. The analytical methods used are as follows:
X-RAY CRYSTALLOGRAPHY 15

1. PgCv A portion of the sample was dissolved with 

nitric acid, and after a preliminary separation as ammonium phosphomolybdate, weighed as Mg2P2O7 .

2. F,C1. Both fluorine and chlorine were determined on 

the combined filtrates from two successive sodiumcarbonate fusions and water leaches of another fraction of the sample. Fluorine was weighed as CaF2 

(Groves, 1951) and chlorine as AgCl. Because of the 

apparent low fluorine value (9.03 percent) obtained 

by this method, another fluorine determination by 

the specific-ion-electrode method was made; this 

value (10.3 percent) is the one reported in table 5.

3. FeO. The wagnerite sample was not noticeably affected by boiling for 15 minutes with 1:8 sulfuric acid, 

the usual method of attack for the determination 

of FeO. However, the mineral was completely dissolved by heating for 24 hours at 65°C in 1:15 hydrochloric acid, to which a measured excess of standard 

potassium dichromate had been added to react with 

released ferrous iron.

4. H2O. Total water was determined by the Penfield 

method.

5. MgO, CaO, A12O3 , Fe2O3 , TiO2 , MnO, and insoluble. 

Nitric acid was used to dissolve the sample for these 

determinations. Repeated evaporations to dryness 

with the acid were necessary to completely dissolve 

the wagnerite. After a small insoluble fraction had 

been removed, the filtrate was evaporated to dryness 

so that the interfering phosphorus could be separated by a double extraction with sodium-carbonate 

fusion and water leach. Conventional methods then 

were used for the determination of the cations 

(Peck, 1964).

Chemical analysis and formula. The analysis, after 

correction for impurities (fluorapatite, sillimanite, rutile, 

and quartz), led to the formula (Mg, Fe, Mn)2 03 PO4 

(F,C1) 0.96, with Mg:Fe:Mn=0.97:0.02:0.01, close to the 

empirical formula Mg2(PO4 )F. The presence of sillimanite, rutile, and quartz as impurities in the analyzed 

sample was confirmed by X-ray powder patterns taken of 

the insoluble residue obtained from digestion of part of the 

sample in nitric acid. Fluorapatite as a contaminant in the 

analyzed sample was suspected, but its presence could not 

readily be verified inasmuch as it probably was dissolved 

during analytical procedures. However, energy-dispersive 

microprobe analyses of five polished grains of carefully 

selected, pale-yellow, transparent fragments of wagnerite 

were made by Robert B. Finkelman of the U.S. Geological 

Survey. The results given in table 6, showing an absence of 

Ca in the pure mineral, provide semiquantitative data that 

support the corrections made for impurities including 

the subtraction of a fluorapatite phase in recalculating 

the chemical analysis. (See table 5.)

TABLE 6. Microprobe analysis of wagnerite

from Santa Fe Mountain, Colorado

(semiquantitative data)

[Analyst, Robert B. Finkelman 1

Constituents' Weight percent

(average of 5 grains)

MgO.. 

FeO... 

MnO. 

P205 ..

50 

2

= 1 

40

'Si, Al, Ca, and Ti were below the limits of detection 

(=» 0.5 percent). Fluorine could not be observed in this 

system.

The analysis of the Santa Fe Mountain wagnerite is 

compared in table 5 with other wagnerite analyses 

reported in the literature.

X-RAY CRYSTALLOGRAPHY

Single-crystal X-ray data. Single-crystal X-ray study, 

made by the precession method, was carried out on a 

transparent, equant, pale-yellow fragment of wagnerite 

from Santa Fe Mountain, Colo. The precession photographs confirmed the monoclinic symmetry and space 

group P2/a (for c < a) and yielded the following preliminary crystallographic data: a = 11.94±0.01 A, 

6=12.68±0.01 A, c = 9.65*0.01 A, 0=108°10'±20'. The 

refined cell values, obtained by a least-squares refinement 

of the powder data (Appleman and Evans, 1973), are in 

excellent agreement with those reported by Coda, 

Guiseppetti, and Tadini (1967) for wagnerite from 

Werfen, Austria (table 7). The specific gravity calculated 

for wagnerite from the refined cell data is 3.16, in good 

agreement with the measured value (3.13) obtained on a 

500-mg sample by the pycnometer method.

Precession photographs of the Colorado wagnerite 

showed the presence of a strong monoclinic subcell with 

the 6-axis halved (6.335 A); this subcell is in space group 

72/a, with Z=8, which data confirm the observations of 

Coda, Guiseppetti, and Tadini (1967). The cell parameters of the subcell of the Colorado wagnerite are 

comparable with those reported in the literature for the 

triplite-group minerals triplite, (Mn, Fe, Mg, Ca)2 (PO4 ) 

(F,OH) (Waldrop, 1969), and zwieselite, (Fe, Mn, Mg, Ca) 2 

(PO4 ) (F, OH) (C. T. Tennyson, in Strunz, 1970, p. 316).

X-ray powder data. An X-ray powder diffraction 

pattern of the wagnerite from Santa Fe Mountain, Colo., 

was taken in a Debye-Scherrer powder camera fitted with a 

Wilson adapter (114.59 mm dia.) in Fe/Mn radiation 

( AFe£a =1.9373 A). Film measurements were corrected 

for expansion; the intensities of the observed lines were 

estimated visually by comparison with a calibrated 

intensity strip. Indexed X-ray powder-diffraction data for 

the Colorado wagnerite are cited in table 8 where they are 

compared with data for the calculated powder pattern of
16 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

wagnerite from Werfen, Austria (based on the structural 

data of Coda and others, 1967); also, with data for 

wagnerite from Bamle, Norway (Henriques, 1957); from 

Kyakhta, U.S.S.R. (Finko, 1962); and from Dolni Bory, 

western Moravia, Czechoslovakia (Stanek, 1965).

Identity of ferroan wagnerite with magniotriplite. Wagnerite, ferroan wagnerite, magniotriplite, 

triplite, and zwieselite are fluophosphates with the 

chemical formula X2(PO4 )F, where X=Mg, Fe+2, Mn+2, 

and (or) Ca. In wagnerite, ferroan wagnerite, and magniotriplite, Mg is the dominant cation, generally with lesser 

amounts of Fe+ 2, Mn+2 , and Ca substituting in part for 

Mg; the dominant cation in triplite is Mn+2; in zwieselite 

the dominant cation is Fe+2 . In these minerals, (OH)" 1 

may substitute in part for F" 1 . Strunz (1970) includes 

triplite, zwieselite, and wagnerite in the triplite series, a 

subgroup of the triplite-triploidite group. On the basis of 

recent crystallographic data (table 7), the minerals in the 

triplite series can be divided into two subgroups: (1), one 

containing magniotriplite, triplite, and zwieselite, with 

the b axis « 6.5 A and symmetry 72/fl; (2), the other 

containing wagnerite, with the b axis * 12.5 A and 

symmetry P2i/fl. Comparison of the structures of 

wagnerite (Coda and others, 1967) and triplite (Waldrop, 

1969) indicates that the minerals are not isotypic; Waldrop 

(1969) noted that triplite and zwieselite show identical 

reflection intensities and, on this basis, suggested that they 

are isotypic.

Ferroan wagnerite from Hallsjoberget (Horrsjoberget), 

Sweden (Henriques, 1957) formerly talktriplite of 

Igelstrom (1882) and from pegmatites of the Alberes 

massif, eastern Pyrenees, France (Fontan and others, 1970), 

and magniotriplite from Turkestan ridge, U.S.S.R. 

(Ginzburg and others, 1951), were identified as such solely 

on the basis of X-ray powder photography and chemical 

analysis. As far as is known, magniotriplite and so-called 

"ferroan wagnerite" have never been characterized crystallographically. Because of their high magnesium content, 

ferroan wagnerite from both of the localities and magniotriplite (type material) were examined by X-ray powder 

diffraction and single-crystal techniques in order to 

establish their structural relation to wagnerite and (or) 

triplite.

X-ray powder diffraction patterns of wagnerite, ferroan 

wagnerite, magniotriplite, and triplite are compared in 

figure 17. It is interesting to note that the patterns of the 

two ferroan wagnerites and the magniotriplite are 

identical and show a closer resemblance in spacings to the 

pattern of wagnerite than to that of triplite. The powder 

pattern of wagnerite, however, is visually distinguishable 

from the powder patterns of ferroan wagnerite and 

magniotriplite by the presence of a line at 5.66 A (table 8). 

This line also clearly showed up on films taken of 

wagnerite from Bamle,Norway (USNM C4151), Salzburg, 

Austria (USNM C4150), and Werfen, Austria (USNM

75.

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SP

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ts

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X-RAY CRYSTALLOGRAPHY 

TABLE 8. X-ray powder diffraction data for wagnente, Mg2 (POlj)F

17

This report

hkl

200

120

021

002

202

221

122

310

221

230

122

320

202

032

213

T41

132

402

400

141

330

223

410

240

023

421

T33

242

233

232

341

033

051

204

322

333

214

430

Il4

423

421

251

512

004

314

143

014

152

T24

341

223

510

242

052

522

332

252

431

513

404

Hbllgraben, near 

Werfen, Austria

Calculated Pattern1

dhkl

(A)

5.676

5.535

5.212

4.578

4.280

4.235

3.827

3.626

3.537

3.390

3.289

3.249

3.117

3.105

3.308

2.973

2.845

4.845

2.838

2.825

2.819

2.806

2.770

2.767

2.750

2.704

2.557

2.547

2.515

2.509

2.476

2.474

2.444

2.400

2.366

2.365

2.359

2.356

2.353

2.332

2.324

2.316

2.309

2.289

2.268

2.256

2.253

2.242

2.240 

2.239

2.239

2.235

2.223

2.218

2.202

2.183

2.182

2.151

2.147

2.140

Santa Fe Mountain, 

Colorado

1

6

2

5

2

1

7

3

1

5

1

54

9

67

1

1

100

1

80

4

4

1

18

1

3

21

17

2

1

2

2

3

1

1

1

5

2

3

1

1

3

9

1

1

17

4

19

2

1

8 

5

3

1

21

1

44

1

2

1

1

13

Calculated2

dhkl

(A)

5.662

5.529

5.209

4.577

4.275

4.228

3.825

3.618

3.532

3.385

3.287

3.243

3.114

3.104

3.036

2.970

2.843

2.839

2.831

2.823

2.815

2.804

2.763

2.765

2.749

2.698

2.556

2.545

2.513

2.506

2.472

2.473

2.442

2.399

2.363

2.363

2.357

2.352

2.352

2.328

2.320

2.314

2.304

2.289

2.266

2.255

2.252

2.241

2.2391 

2.236J

2.237

2.230

2.221

2.217

2.198

2.181

2.180

2.147

2.143

2.138

Observed9

dhU * 

(A)

5.662 7

5.2H 7

4.226 11

3.827 5

3.533 '"s

3.287 60

3.244 5

3.114 60

2.970 100

2.839 85

2.804 "il

2.766 "'3

2.748 30

2.697 21

2.555 5

2.468 15

2.363 '"7

2.289 '"S

2.251 6

2.239 6

2.220 "'6

2.T97 "il

2.137 4

Henriques (1957) Finko (1962) Stariek (1965)-

Dolni Bory, 

Bamle, Norway ^ ta> western Moravia, 

U-S-S'R- Czechoslovakia

Observed* Observed*

dhkl 1 *hkl

(A) (A)

5.635 20

5.170 10 5.18

4.208 10 4.20

4.015 10 3.81

3.527 "ib 3.53'

3.279 80 3.33

3.236 20

3.107 90 3.15

2.968 100 2.99

2.836 ibb 2.85'

2.799 '40 2.78

2.762 "30 2.72

2.744 50

2.695 60

2.544 20 2.57

2.472 50 2.49

2.378 "ib 2.42

2.238 20 2.25

2.T97 50 2.2i

Observed*

1 dhkl

(A)

5.64

"30 5.23

40 4.25

20 3.87

'40 ......

90 3.29

90 3.12

100 2.97

ibb 2.84

60 2.80

"30 2.76

2.69

2.62

10 2.55

30 2.47

10 2.38

20 2.24

"40 2.19

1

10 "ib

20

10

70

80

100 "90

50 "so

70

20

20

30

"ib

40

"so

See footnotes at end of table, p. 19.
18 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN. COLORADO

TABLE 8. X-ray powder diffraction dataforwagnerite, Mg2(PO4 )F Continued

hkl

520

343

442

114

134

124

602

T62

160

143

061

552

334

204

544

214

261

621

044

360

523

362

343

?44

025

263

?25

522

630

541 4*61

324

244

M5

461

206

080

T64

263 

602

720

106

364

225

625

280

345

S02

741

282

743

326

823

606

265

804

800

381

Hollgrahen, near 

Werfen, Austria

Calculated pattern1

dhkl

(A)

2.137

2.121

2.117

2.090

2.083

2.009

1.9820 

1.9810

1.9341

2.077 

2.073

2.059

2.055

2.024

1.9237

1.9136

1.9020

1.8932

1.8902

1.8558

1.8450

1.8172

1.8100

1.7954

1.7737

1.7593

1.7512

1.7504

1.7488

1.7374

1.7261

1.7255

1.6712

1.6446

1.6288

1.6134

1.6055

1.5849

1.5844

1.5840 

1.5820

1.5712

1.5645

1.5577

1.5532

1.5409

1.5265

1.5064

1.4946

1.4917

1.4863

1.4741

1.4633

1.4376

1.4268

1.4246

1.4226

1.4190

1.4171

This report Henriques(1957) Finko(l962) Stanek (1965)

Santa Fe Mountain, 

Colorado

1

1

6

15

2

1

1

11 

15

4

14 

11

26

1

1

24

9

4

5

20

6

6

7

4

11

5

9

4

6

9

19

5

21

25

4

7

4

5

5

4

25 

21

11

6

28

16

20

12

8

5

4

8

7

13

11

8

7

4

6

14

Calculated2

dhkl

(A)

2.133

2.119

2.114

2.089

2.083

2.009

1.97711 

1.9793J

2.076 1 

2.076 j

2.058

2.053

2.022

1.9226

1.8856

1.8551

1.8430

1.8134

1.7925

1.7719

1.7589

1.7365

1.6698

1.6436

1.6278

1.5829 1 

1. 5790J

1.5675

1.5566

1.5524

1.5387

1.5253

1.5048

1.4852

1.4711

1.4620

1.4343

1.4251

1.4T58

Observed'

dhkl

2.T14

1.9782

2.076

2.058

1.9229

1.8856

1.8552

1.8428

1.8J28

1.79 is

1.7720

1.7585

1.7368

1.7233

1.6701

1.6440

1.6275

1.5831

1.5673

1.5565

1.5526

1.5388

1.5253

1.5054

1.4862

1.4717

1.4619

1.4341

1.4253

1.4'i 57

1

1

15

13

7

11

18

4

3

5

11

4

11

5

11

11

5

11

11

4

'is

18

7

6

2

7

7

5

4

5

7

Dolni Bory, 

Bamle, Norway Kyakhta, western Moravia, 

LJ.S.S.R. _ . . . . Czechoslovakia

Observed4

dhkl

(A)

2.1 ii

1.979

2.071

2.057

1.922

1.915

1.894

1.887

L794

1.739

l'.725

1.670

......

1.585 

1.580

L558

1.554

1.541

1.528

1.507

l'.489

1.474

1.464

1.426

1.4 i 7

Observed5

' dhkl

(A)

'20 2.13

30

30 2.09

30 1.995

10

10 1.905

10 '.'.".".

30 1.859

20 1.805

10 1.757

30 1.733

30 1.684

20 1.594 

30 1.587

20 1.567

20 1.555

10 1.538

20

10

20 1.494

20 1.474

10

10 1.425

20 ..'.'.'.'.

Observed'

(A)

30 2.12

1.977

70 2.08

70 2.06

1.929

60

30 1.888

"" 1.834

20 1.793

1.771

40 1.747

50 1.724

50 1.670

1.632

60 1.585 

70

70 1.558

30

50 1.541

1.528

30 1.488

80

1.467

1.448

20

.... 1.421

1

"20

50

40

40

60

80

10

30

10

20

30

50

20

60

60

20

10

40

30

40

See footnotes at end of table, p. 19.
ORIGIN 19

TABLE 8. X-ray powder diffraction data for wagnerite, Mg2(PO4)F Continued

Hbllgraben, near 

Werfen, Austria

Calculated Pattern1

This report

Santa Fe Mountain, 

Colorado

Calculated2 Observed'

Henriques (1957)

Bamle, Norway

Observed4

Finko (1962)

Kyakhta, 

U.S.S.R.

Observed5

Stan?k (1965)

Dolni Bory, 

western Moravia, 

Czechoslovakia

Observed'

hkl

663 1

446 1

444 1

482 1

065 1

465 1

463 1

722 1

842 1

661 1

345

762

425

726

583

265

665

147

2" 10 1

1 102

366

284

385

680

941

3 100

dhu

(A)

.4116

.4029

.3987

.3846

.3839

.3795

.5763

.3641

.3519

.3466

.3385

.3277

.3268

.3122

.2816

.2766

.2698

.2409

.2376

.2259

.2253

.2232

.2167

1.2150

1.2077

1.2022

7

4

9

12

5

15

8

14

9

9

8

7

6

5

10

8

14

8

9

5

7

9

5

4

13

13

6

dhU

(A)

1.3973

1.3834

1.3749

1.3615

1.3489

1.3445

.3376

.3253 1

.3256J

.3104

.2802

1.2759

1.2251J

1.2243J

1.2'i'S2

1.2049

dhkl

(A)

1.3982

1.3832

1.3747

1.3616

1.3489

1.3438

1.3382

1.3256

1.3104

1.2801

1.2758

1.2251

1.21 41

1.2054

I dhkl I *hU 7 dhU 7

(A) (A) (A)

3D ".".". ....

"'j l".385 30 1.384 80 1.384 40

"9 1.376 10 1.348 50 1.363 20

3

3

3

3

2

5 ...... .... 1.322 30

4 ...... .... 1.284 80

4

4 ...... .... 1.232 60

6 '.'."." .... 1.220 70 ...... ...'.

5 ...... .... 1.210 60

(Plus eleven 

additional lines.)

(Plus additional 

lines.)

'Calculated from the crystal structure data of Coda, Guiseppetti, Tadini (1967) in space 

group P2,/a: a = 11.957 A, 6 = 12.679 A. c = 9.644 A., 0 = 108° 18'. All possible calculated 

dhU value* listed for d ^ 2.000 A, for calculated intensities with / * 1; calculated 

dhkl va'ues f°r <1 * 1.9999 A given only for those with / * 4. Calculated integrated 

intensity data normalized to a maximum of 100.

'Calculated from these unit-cell parameters obtained from least-squares refinement of 

the observed X-ray powder data with fixed indexing by use of the computer program 

of Appleman and Evans (1973): a = 11.926 A, 6 = 12.671 A, c = 9.641 A, ft = 108°

17'. All possible calculated dfcw values listed for d * 2.000 A; calculated dhkl values 

for d « 1 .9999 A listed only for those observed.

'Camera diameter, 114.59 mm. Mn-filtered Fe radiation (A FeKa =1.9373 A). Wilsontype pattern. Film shrinkage negligible. Intensities estimated visually by direct comparison 

with a calibrated intensity film strip. D = diffuse.

4Guinier camera. CuKa radiation.

'Sample 112, pale yellow. Camera diameter, 57.3 mm. Unfiltered Fe radiation.

'Camera diameter, 114.6 mm. Mn-filtered Fe radiation ( XFeAfa = 1.9373 A).

R5306), when taken in iron radiation, but it was not 

present in any of the patterns taken of triplite from 18 

different localities. The line at 5.66 A should be looked for 

in distinguishing patterns of wagnerite from those of the 

triplite series.

Preliminary crystallographic data for ferroan wagnerite 

and magniotriplite, based on precession photography, are 

given in table 7 where they are compared with data for 

wagnerite and triplite. Comparison of these data indicates 

that despite their high Mg content both the ferroan 

wagnerite from Hallsjoberget, Sweden, and the Alberes 

massif, eastern Pyrenees, France, and the magniotriplite 

from the Turkestan ridge, U.S.S.R., are isostructural with 

triplite. Refined cell parameters and indexed powder data 

for both ferroan wagnerites and magniotriplite (Mrose, 

unpublished data) lead to the conclusion that the so-called 

"ferroan wagnerite" is actually magniotriplite, the Mgdominant member of the triplite series, and that, therefore,

this material should not be referred to as ferroan 

wagnerite.

ORIGIN

The origin of the wagnerite at Santa Fe Mountain is 

linked inseparably with the origin of light-colored rutilebearing Precambrian gneisses in the east-central Front 

Range. Although the genetic history of these rutilebearing gneisses is admittedly debatable, we think that 

their field relations and their chemical and petrographic 

characteristics suggest very strongly that they were 

originally products of subaerial weathering (Marsh and 

Sheridan, 1976). According to this hypothesis, intense 

weathering of tuffs and flows of intermediate to basic 

composition occurred at several different times during the 

accumulation of a thick succession of volcanic and sedimentary rocks in Precambrian time. The resulting 

weathered products were bentonitic clays enriched in
20 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN. COLORADO

FIGURE 17. X-ray powder photographs with Fe/Mn radiation (camera diameter: 114.59 mm): A) wagnerite, Santa Fe Mountain, 

Colo.; B) ferroan wagnerite (formerly talktriplite of Igelstrom, 1882), Hallsjoberget (HorrsjcJberget), Sweden; C) ferroan 

wagnerite, Alberes massif, eastern Pyrenees, France; D) magniotriplite, Turkestan ridge, U.S.S.R. (Fersman Mineralogical 

Museum, Moscow; type material); £) triplite, Chatham, Conn. (USNM 93792; analyzed material).

titania (leucoxene), alumina (clay), and silica (clay and 

quartz) as compared to the unweathered volcanic rocks. 

Surface waters partly reworked these clays, distributing 

them as thin layers and lenses of somewhat variable 

composition. Various amounts of sedimentary materials 

were added to the clays and interlayered with them. 

Fluorine of probable volcanic source was adsorbed by the 

weathered products in varying amounts in different 

localities. After accumulation of additional layers of

volcanic and sedimentary rocks, high-grade regional 

metamorphism took place throughout a long and 

complex period of Precambrian tectonism. Early in this 

period, the weathered products and their admixtures 

recrystallized to several varieties of rutile-bearing gneiss, 

some rich in sillimanite and quartz, some characterized by 

pale biotite and soda-rich plagioclase, and others gradational between these types. Wagnerite crystallized contemporaneously with fibrolitic sillimanite, biotite, and
ORIGIN 21

plagioclase in a local variant of the rutile-bearing gneiss. 

Foliation and lineation were formed in all the metamorphosed rocks during this early stage of crystallization. 

Somewhat later, this same long period of regional metamorphism culminated in conditions that promoted the 

growth of coarse crystals of some of the minerals. A certain 

amount of redistribution of fluorine, a type of fluorine 

metasomatism, occurred within the rutile-bearing layers. 

Coarse crystallization was enhanced by these volatiles. In 

some areas, such as the area described initially by 

Sheridan, Taylor, and Marsh (1968), topaz crystallized 

during concurrent growth of prismatic sillimanite. At the 

Santa Fe Mountain locality, large crystals of corundum, 

aggregates of prismatic sillimanite, and the larger grains 

of wagnerite were formed. During this same stage of 

crystallization, rims of apatite developed on wagnerite. 

Sericite and chlorite formed in a lower grade metamorphic environment, either during a retrograde stage of 

waning metamorphic intensity or perhaps during an even 

later event.

The origin of the principal types of Precambrian metamorphic rock in the east-central Front Range is, of course, 

fundamental to the genetic history of the wagnerite 

locality. Biotite gneiss, commonly sillimanitic, is one of 

the principal rocks in this region and was considered by 

Ball (in Spurr and Garrey, 1908, p. 44) to represent metamorphosed shaly sediments. Subsequent investigators 

have agreed with this conclusion and have considered the 

sillimanitic varieties as representing alumina-rich shales 

and the nonsillimanitic varieties as representing sandy 

shales or graywackes. The origin of feldspar-rich gneiss, 

the other principal metamorphic rock in this region, has 

been more problematical. Given various names, such as 

quartz monzonite gneiss and microcline gneiss, the 

feldspar-rich gneiss has been considered as an old intrusive 

igneous rock (Lovering and Goddard, 1950, p. 23) and as a 

metasedimentary rock (Moench and others, 1962, p. 38; 

Sheridan and others, 1967, p. 23). Hedge (1969, p. 12, 

120-123) considered the feldspar-rich gneiss to be metamorphosed felsic volcanic rock because the gneiss is 

similar in chemical composition to acid volcanic rocks 

found in island arc association with basalts. Hornblende 

gneiss and amphibolite, also abundant in parts of this 

region, very likely were originally intermediate to basic 

tuffs and flows, and calc-silicate gneiss and impure marble 

were sedimentary rocks ranging in character from 

calcareous shale to argillaceous limestone. The early Precambrian history in this region, therefore, probably 

involved an accumulation of a thick, layered succession 

composed predominantly of volcanic and sedimentary 

rocks.

Thin layers and lenses of light-colored rutile-bearing 

gneiss occur at several stratigraphic levels in the Precambrian terrane of the east-central Front Range. The

distribution, characteristics, and probable origin of these 

rutile-bearing gneisses have been discussed by Marsh and 

Sheridan (1976). Sillimanite-quartz gneiss, one of the 

principal varieties of rutile-bearing rock, has a simple but 

unusual mineral and chemical composition, containing 

very little else except quartz, sillimanite, and accessory 

rutile; it is chemically similar to many bentonitic clays. 

Rankama and Sahama (1950, p. 209, 563) have noted that 

clays produced by weathering are commonly low in 

calcium and high in aluminum and titanium. 

Serdyuchenko (1968) believed that metamorphic rocks 

containing kyanite, sillimanite, or corundum in many 

places in the world are metamorphosed kaolinite-bauxiteweathering crusts. Kyanite-quartz rock in India was considered by Dunn (1929, p. 248) to have been originally a 

surface decomposition of basalt to bauxitic clay. 

Espenshade and Potter (1960, p. 24-25) concluded that 

sediments containing clay or bauxite were the precursors 

of kyanite quartzite and sillimanite quartzite in some districts of the southeastern United States. Topax is present 

in notable amounts in some of the rutile-bearing rocks in 

the east-central Front Range, emphasizing the local 

importance of fluorine. It is likely that volcanic emanations provided this fluorine to the original weathered 

materials. In support of this hypothesis is the observation 

of Rankama and Sahama (1950, p. 764) that fluorine is 

added to the "exogenic cycle by volcanic processes" and 

that fluorine is strongly adsorbed in soils, bentonite, and 

bottom muds.

Although the details of the very early history of the 

rutile-bearing gneisses in the Front Range are matters 

involving considerable speculation, the present characteristics of these gneisses are the result of high-grade regional 

metamorphism. The rutile-bearing gneisses occur as persistent stratum-like layers and lenses in a thick succession 

of gneisses whose mineralogy, textures, and structural features all give evidence of folding and metamorphic 

recrystallization under high temperature and pressure. 

The regional character of the metamorphism, rather than 

a "contact" phenomena, is indicated by the absence of 

adjacent bodies of igneous rock. The high grade of metamorphism is indicated by the abundance of sillimanite in 

the light-colored gneisses and by the common presence of 

the pair sillimanite-microcline in pelitic gneiss layers of 

this region.

The texture and mineralogy of the wagnerite-bearing 

sillimanite-plagioclase gneiss indicate that all the 

minerals, except sericite and chlorite, are products of the 

regional high-grade metamorphism. The appearance of 

the rock, with its coarse prismatic sillimanite and the large 

grains of corundum diversely oriented in a foliated matrix 

of finer minerals, is similar in many respects to the 

porphyroblastic textures observed in other gneisses of this 

region. For example, calc-silicate gneiss and impure
22 WAGNERITE OCCURRENCE, SANTA FE MOUNTAIN, COLORADO

marble locally contain large porphyroblasts of garnet, 

epidote, and other minerals. Similarly, large randomly 

oriented porphyroblasts of andalusite occur in the mica 

schist unit of the nearby Ralston Buttes district (Sheridan 

and others, 1967, p. 8) 17 km northeast of the Santa Fe 

Mountain locality. We believe that such porphyroblasts 

developed in local sites where local pressure-temperature 

conditions and volatile concentrations favored the growth 

of coarse crystals late in the regional metamorphism.

Although bodies of pegmatite are present at the Santa Fe 

Mountain locality, they are not genetically related to the 

wagnerite. The pegmatites are of simple quartz-feldspar 

composition and contain no wagnerite.

The occurrence of wagnerite as a regional metamorphic mineral at Santa Fe Mountain is believed to be 

the direct result of the rather abnormal composition of the 

light-colored gneiss in which it is found. Apatite, not 

wagnerite, is the ubiquitous phosphate-bearing mineral 

in all the other gneisses. A calcium deficiency in the 

wagnerite-bearing gneiss is inferred from the high Na:Ca 

ratio of the plagioclase and the paucity of other calciumbearing minerals. Although some apatite is present in the 

gneiss, calcium in the rock was apparently insufficient to 

accommodate all the available phosphate. The wagnerite 

further reflects the high Mg:Fe ratio, consistent with the 

pale biotite that is rich in Mg and deficient in Fe as 

compared with the biotite in most other gneisses of this 

region.

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