UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 931-P

MICA-BEARING PEGMATITES 

OF NEW HAMPSHIRE

A PRELIMINARY REPORT

BY 

J. C. OLSON

Strategic Minerals Investigations, 1941 

(Pages 363-403)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1942

For Bale by the Superintendent of Documents, Washington, D. C. -------- Price 25 cents

CONTENTS

Page

Abstract................................................. 363

Introduction............................................. 364

Previous work........................................ 365

Field work and acknowledgments....................... 366

Geology.................................................. 367

Grafton district...................................... 368

Alstead area, Keene district......................... 368

Mica-bearing pegmatites.................................. 369

Size................................................. 369

Relation to older rocks.............................. 369

Relation to faults.................................... 370

Mineralogy.'.......................................... 371

Mineral zones and streaks............................ 373

Mica..................................................... 374

Localization......................................... 374

Physical properties and uses......................... 376

Staining....................o.................... 377

Flexibility...................................... 377

Cleavage......................................... 377

Intergrowths with other minerals................. 378

Color............................................ 379

Dielectric constant.............................. 379

Power "factor..................................... 380

Sheet mica sizes and pric'es.......................... 382

Punch mica....................................... 382

Sheet mica....................................... 383

Past production...................................... 383

Cost of mining....................................... 385

Possible future production........................... 385

Mines.................................................... 387

ILLUSTRATIONS

Plate 61. Geologic map of the Alstead area, Keene district , New Hampshire........................

62. Map showing locations of mica and feldspar 

mines of the Grafton district, New Hampshire .......................................

63o Map showing locations of mica and feldspar

mines of the Keene district, New Hampshire.. 

Figure 38. Index map of New Hampshire showing locations

of the Grafton and Keene districts..........

39. Sketch map of the Valencia minob..............

40. Plan of the Palermo mine......................

Ill

370

390

390

365

389

391
IV ILLUSTRATIONS

Figure 41. Sketch map of the Danbury mine...........

42. Sketch map of the Strain mine............

43. Sketch map of the Standard (Belden) mine,

44. Sketch map of the Big mine...............

45. Plan of the French mine..................

Page

393

394,

396

400

402

TABLES

Table 5. Power factors of New Hampshire muscovite.....,

6. Size distribution and price ranges of trimmed 

domestic sheet mica.................... ...,

7. Production of sheet and punch mica in New

Hampshire, 1908-39..........................

8.' New Hampshire mica and feldspar mines, with 

notes on the character and occurrence of 

the mica....................................

Page 

381

383

384

388
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 

A PRELIMINARY REPORT

By J. C. Olson

ABSTRACT

Mica has been mined in New Hampshire since 1803. Production 

from 1908 through 1939 has aggregated 13,326,990 pounds of sheet 

and punch mica, an annual average of 416,470 pounds. Since 1931 

production has been below this average, because of economic conditions rather than depletions.

The mica-bearing pegmatites of the Grafton and Keene districts occur mostly in sillimanite-mica schist adjacent to large 

areas of biotite gneiss. The pegmatite bodies range from a 

fraction of an inch to more than 200 feet in thickness; moat of 

them are crosscutting, and about 75 percent strike northeast. 

Mica occurs sporadically in most of them but where present in 

commercial quantities it is localized in one or more of the following zones: (1) In quartz-plagioclase-muscovite zones 2 to 10 

feet from the walls of large pegmatite bodies, (2) in or near 

quartz masses that occur mostly near the centers of the bodies, 

(3) in thin dikes 5 to 15 feet thick or in similar offshoots 

from larger bodies, (4) within large pegmatite bodies, in more 

or less tabular streaks or zones composed principally of plagioclase, quartz, and muscovite.

Sixty-seven mica and 18 feldspar mines and prospects were 

examined in the Grafton district, 16 mica and { 29 feldspar mines 

in the Keene district, and l.mica mine in Strafford County. Six 

of the feldspar mines and two of the mica mines were in operation at the time of the writer's visit, in the fall of 1940. 

Mica from 60 percent of the 131 mines was of a light-amber color. 

Pegmatites that contain abundant biotite generally yield mica 

that is of a light-amber or ruby color; those that contain abundant cleavelandite or lithium minerals commonly yield a light 

yellowish-green mica.

Tests made by the National Bureau of Standards on 76 samples 

of carefully selected sheet mica from 65 of the mines indicate 

that this sheet mica meets the exacting specifications for certain electrical uses.

Only a general estimate of reserves can be made because of 

the erratic distribution of mica in pegmatites. On the basis of 

an average annual production of 416,470 pounds of sheet and 

punch mica over the 32-year period 1908-39, it is estimated that 

an annual production of 500,000 pounds of sheet and punch mica, 

of which from 100,000 to 125,000 would be sheet, could be maintained for several years at a cost slightly higher than the 

average of the past. With more intensive development, a possible annual production of 1,000,000 pounds or more of sheet and 

punch mica might be attained.

363
364 STRATEGIC MINERALS INVESTIGATIONS, 1941

INTRODUCTION

Mica in some form is used as an insulating material in 

nearly all electrical equipment. The poorer grades appear in 

many common household appliances. Sheet mica of the best grades 

has been used mainly for radio transmitter condenser films, for 

receiver and trimmer condenser films, for radio tube supports 

and bridges, and in airplane motor spark plugs. Of greater 

quantitative importance than sheet mica are the thin films of 

mica about 0.001 inch thick known as splittings, used in the 

manufacture of mica board or built-up mica. Splittings are not 

ordinarily produced in the United States because of the high 

cost of the labor necessary to split the mica. High-grade sheet 

mica and splittings have been obtained in the past mainly from 

foreign sources, principally India, and are therefore regarded 

as strategic materials The present investigation is directed 

toward determining, insofar as possible, to what extent the pegmatites of New Hampshire could supply such mica.

Mica has been mined from New Hampshire pegmatites since 1803. 

The principal mines are in two areas, hereafter referred to as 

the Keene and Grafton districts (see fig. 38), that include the 

productive parts of a belt of pegmatites extending northwestward 

from Cheshire County through Sullivan and Merrimack Counties 

into Grafton County. Mica has also been produced from Strafford 

and Coos Counties.

The main belt of mica-bearing pegmatites follows approximately the divide between the Connecticut and Merrimack Rivers, 

in a glaciated region of wooded hills and numerous lakes and 

.ponds, in which altitudes range from 650 to 2,100 feet. Bold

outcrops of resistant pegmatite are prominent topographic featiUr98« Graded, town roads and paved highways make all parts of 

the mica districts accessible, although many of the roads to 

woodlands and abandoned farms are overgrown and covered with 

fallen timber. The Boston and Maine Railroad, which serves the
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 365

western part of New Hampshire, has stations in the mica districts at Canaan, Grafton, Danbury, Plymouth, Rumney, Newport, 

Walpole, and Keene.

\ C A R R O L L

B E L K N A P

M E R R I MSA C K X

^. R n C K I NGHAM

MASSACHUSETTS

Figure 38. Index map of New Hampshire showing locations of the Grafton and

Keene districts.

Previous work

A comprehensive report on the geology of New Hampshire, in 

which the mica deposits and their association with sillimanitemica schist were discussed, was published by Hitchcock ^in 1877. 

Sterrett examined many of the mica mines in 1914, and included

I/ Hitchcock, C. H., The geology of New Hampshire, Concord, N. H., 18J7.
366 STRATEGIC MINERALS INVESTIGATIONS, 1941

2/

his descriptions in a report on mica deposits of the United

States. In the last decade, the geology of a large part of

§/

Field work was carried on by the writer during 3^- months in 

the fall of 1940, with the assistance of P. W. Hinrichs for l£ 

months and of R. I. Edwards for 2 months. Practically all the 

feldspar and mica mines in the area, a total of 131, were examined and located on topographic maps having a scale of 1:62,500; 

and an area of about 2 square miles, at Alstead in the Keene 

district, was mapped on a scale of 1:24,000 to show the extent 

and structural relations of the pegmatites. The work was under 

the supervision of T. L. Kesler, who accompanied the writer during 2 weeks of preliminary reconnaissance. Miners and other 

residents of the mica districts helped the party to find mines 

and to reconstruct local mining history. Messrs. L. P. Crowe, 

of the General Electric Co., and Paul French, of Eugene Munsell 

& Co., kindly gave permission to publish company production figures. Production records of the Bureau of Mines, United States 

Department of the Interior, were made available by Messrs. P. M. 

Tyler and K. G. Warner. To Mr. Tyler the writer is especially 

indebted for suggestions and criticisms concerning procedure for

testing mica samples 

2/ Sterrett, D. B,, Mica deposits Of the United States: U. s. ceoi. 3ur-

-»-<=>y Siil. 7*4Q. 1923.

2/ Billings, M. P., Geology of the Llttleton ana. Moooiitvuic*, qrtadretitsie«,.

N, H,: New Hampshire Planning and Development Comm., Concord, N. H., 1935." 

Biin,^, M. i>.. ^,1 fliiiiana. c. R., Geology of the Franconia quadrangle, N. H.J New Hampshire Planning and Development comm., concora, w. H.,

1935. '

Page, L. R. , Geology- of the Rxunney quadrangle. New Hampshire: Unpublished doctorate thesis at the University of Minnesota, 1937.

Chapman, fl. A., Geology of the MfiSCOIflR Quadrangle, Hew Hampshire; 

Geol. Soc. America Bull., 701. 50, pp. 1?7-150, 1339.

Fowler-Limn, Katherine, and Kingsley, Louise, Geology of the Cardigan 

quadrangle, New Hampshire: Geol. Soc. America Bull., vol. Ug, pp. 1363-1386, 

1937.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 367 

GEOLOGY

The oldest rocks in the region are amphibolite, quartzite, 

mica schist and gneiss, sillimanite-mica schist and gneiss, 

staurolite-mica schist,- and other metamorphosed sedimentary 

rocks of Ordovician, Silurian, and Devonian age, which crop out 

over large areas in western New Hampshire. Belts of these rocks 

trend about N. 20° E., the average strike of their foliation, 

which generally dips to the east.

Biotite gneisses, which occur in north to northeast-trending 

belts, appear to have intruded the more schistose rocks as thick 

sills or laccolithic bodies. The gneisses locally grade into 

nonfoliated granitic rock, but in the areas in which mica-bearing pegmatites occur they are distinctly foliated and commonly 

contain large phenocrysts or metacrysts of orthoclase. The 

foliation of the gneiss is conformable in general with that of 

the surrounding schist.

Small intrusive masses of a granite younger than the gneiss 

occur in the eastern part of the Grafton district. Dikes of 

granite, mostly less than 3 feet thick, are abundant in Grafton 

and adjacent towns, where they cut across the foliation of both 

the schist and the gneiss.

The mica-bearing pegmatites appear to be younger than the 

granite dikes. Dikes of basalt, diabase, camptonite, and other 

basic rocks cut all the older rocks.

Prom structural relations the gneiss, granite, and pegmai/ tites are believed to be post-Lower Devonian, probably late

Devonian. The age of the pegmatite at the Ruggles mine has been 

estimated from the lead-uranium ratio to be 304 million years 

(late Devonian).

U/ Billings, M. P., Paleozoic age of the rocks of central New Hampshire: 

Science, new ser., vol. 79,.pp. 55-56, 193^.

3/ Shaub, B. M., The occurrence, crystal habit, and composition of the 

uraninite from the Ruggles mine, near Grafton Center, New Hampshire: Am. 

Mineralogist, vol. 23, pp. 33^-3^1, 1938.

442183 0-42-2
368 STRATEGIC MINERALS INVESTIGATIONS, 1941

Grafton district

In the Grafton district, most pegmatite bodies that have 

been mined for mica are near the contact between biotite gneiss 

and silllmanite-mica schist, principally in the schist. Proximity to this contact suggests a genetic relation between gneiss 

and pegmatite, and is one of the evidences of an Intrusive origin of the gneiss. However, the pegmatites were emplaced after 

the development of foliation in the gneiss, and have undergone 

very little metamorphism. Small bodies of granite enclose some 

of the pegmatites, and have been the source of some of the pegmat it ic material.

Alstead area, Keene district

Typical rocks of the Keene district are exposed in the 

Alstead area, a geologic map of which forms plate 61. At 

Alstead the country rocks generally strike north to N. 10° W., ' 

and dip from 30° E. to vertically. From west to east they consist of: (a) AmphiboJ.ite interbedded with thin layers of 

quartzite; (b) coarse feldspathic biotite gneiss that is partly 

garnetlferousj (c) quartz-mica schist, mica gneiss, and quartzite, containing needles of sillimanite in places. A band in 

which quartzite is most abundant is indicated on the map, although quartzite is also interbedded with other parts of the 

quartz-mica schist. The sillimanite is increasingly abundant 

westward toward the contact with the biotite gneiss, but the 

amount differs considerably in adjacent layers. Pegmatites, as 

much as 200 feet across, strike north to northeast, most of them 

cutting across the foliation of their wall rocks at low to moderate angles. The pegmatites that have produced the most mica 

('the French, Big, and Island mines) are in quartz-mica schist 

containing sillimanite, adjacent to the feldspathic biotite 

gneisso Large pegmatites in other parts of the Alstead area, 

and also to the east and west of the area mapped, have been
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 369 

mined for feldspar, but apparently contain less commercial mica«

6/ the Nichols, Isham, Jehial White, and Bingham Hill mines, are

In wall rocks similar to the schist in which the French, Big, 

and Island mines occur.

MICA-BEARING PEGMATITES * 

Size

The pegmatites range in size from thin pods or stringers to 

large irregular masses such as those at Beryl Mountain, which 

are 200 feet thick, and at Aaron Ledge, which are 250 feet thick, 

and those massive ledges in the west part of the town of Groton, 

whose dimensions are measured in hundreds of feet but which have 

not been mined extensively for mica. Many of the pegmatites are 

more than 1,000 feet long. Thicknesses of individual pegmatites 

are seldom constant even for short distances. The pegmatite at 

the United mine, for example, as much as 20 feet thick in surface outcrop, is said to be only 18 inches thick within a distance of 90 feet down the incline.

Relation to older rocks

Pegmatites that are rich in sheet mica are practically confined to mica schist, sillimanlte-mica schist, and quartz-mica 

schist, and to biotite gneiss adjacent to them. Pegmatites in 

other rocks, such as amphibolite, quartzite, and granite, generally contain less commercial muscovite than those in micaceous 

rocks, and have been mined principally for feldspar.

Most large pegmatites have irregular shapes and cut across 

the foliation of their wall rocks. Pegmatites 10 or 15 feet 

thick and offshoots from the larger masses cut across the

6/ Mines are numbered in table 8 and located by corresponding numbers on 

plates 62 and 63.
370 STRATEGIC MINERALS INVESTIGATIONS, 1941

foliation in -some places and are conformable in others. About 

75 percent of the pegmatites strike northeast, generally between 

N. 10° E. and N. 65° E. Their dips are generally greater than 

60°. Pre-pegmatite jointing may have determined in part the 

location and forms of pegmatites.

The crescent shapes of at least three pegmatites result from 

Injection parallel to folds in the older rocks. At the Kimball 

Hill (India Mica Co.) mine, however,, the mica in the vicinity of 

the fold was mostly bent and broken, according to Sterrett, and 

this may indicate continuation of the folding after the mica 

books had formed.

Introduction of the pegmatite into the country rocks appears 

to have been dominantly an intrusive process. This is Indicated 

by the large size and irregular shape of the bodies, the distortion of wall rocks, and the relatively clean-cut though 

irregular contacts. Contacts with wall rocks are commonly sharp, 

though some are hazy owing to moderate replacement by pegmatitlc 

material, and some inclusions are partly replaced. Inclusions 

are usually parallel to the structure of the adjacent country 

rock, tut some appear to have been rotated.

Relation to faults

Postpegmatlte faults are not common in mica mines, because 

in faulted pegmatites the mica books are likely to be crushed 

and of little or no value as sources of sheet mica. Postpegmatite faults with throws of less than 5 feet were observed, tlOWever, at the Kllton, Powell, and. Evans mines. Ttie mica Is distorted near the faults. A slightly lower proportion of fiat

sheets and a higher proportion of distorted mica in the AcworthEast Alstead area than is usual elsewhere may be a result or

localized postpegmatite deformation.
GEOLOGICAL SURVEY

EXPLANATION

Feldspathic biotite gneiss

Quartz-mica schist 

a.Sillimanite present 

b. Quartzite abundant

Pegmatite

Quarry

X

Mine

X 

Prospect

Strike and dip 

of foliation

1000

I 11

0

I I

GEOLOGIC MAP OF THE ALSTEAD AREA, 

KEENE DISTRICT, NEW HAMPSHIRE

5000 Feet
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 371 

Mineralogy

More than 30 minerals have been reported from the pegmatite 

at the Ruggles mine alone, and many other pegmatites have 

yielded specimens of mlneralogic interest. Only the more abundant minerals are described in this section, Muscovite is not 

included here; its mineral associations and distribution in the 

pegmatites are described in the section on localization of mica 

(p. 374).

Quartz occurs, unevenly distributed, in. every pegmatite, and 

is associated with every pegmatitic mineral. Common gray quartz 

predominates, but rose, white, and clear varieties were seen. 

In general, pegmatites less than 15 feet thick contain a slightly higher proportion of quartz than the thicker bodies. The 

centers of mica-bearing pegmatites are generally quartzose, and 

commonly are marked by discontinuous quartz masses as much as 

15 feet thick which in some places contain crystals of potash 

feldspar, beryl, or muscovite.

Feldspar has been the principal product in 47 of the mines 

examined, and has been a byproduct in many of the mica mines. 

Commercial quantities of feldspar generally are associated with 

massive gray quartz in the central parts of pegmatites. Microcline, the potash feldspar, is the variety generally mined, 

chiefly because it is coarse-grained; it forms blocks as much as 

6 feet long.

Plagioclase is subordinate to potash feldspar in most of the 

pegmatites, but is the dominant feldspar in a few. Wide pegmatites (over 6 feet) seem to contain a greater proportion of 

potash feldspar than some of the thin bodies or offs*hoots from 

larger masses. Plagioclase is most abundant near the walls but 

also occurs in other parts of pegmatites. Cleavelandite, the 

platy variety of albite, is present in minor quantities at more 

than a dozen of the mines examined. It is typically associated 

with tourmaline, yellowish-green muscovite, and apatite, and
372 STRATEGIC MINERALS INVESTIGATIONS, 1941

was found in every pegmatite that contained the lithium minerals 

spodumene, triphylite, and lithiophillte.

Biotite, seen at roughly two-thirds of the mines, is a common constituent. Typical are lathlike strips as much as 5 feet 

long, which appear to have formed in seams or cracks that cut 

through graphic granite, mlcrocline, quartz, and less commonly 

plagioclase. Such biotite strips are especially plentiful with 

graphic granite and mlcrocline. Intergrowths of biotite and 

muscovite are common in pegmatites containing both minerals,'but 

where the quantity of biotite is great, muscovite is less abundant j furthermore, the muscovite commonly splits poorly and is 

called tanglesheet. Most pegmatites mined for mica, therefore, 

contain little biotite, and intergrowths of the two micas are 

relatively scarce at most large mines, though seen at many prospects.

Garnet is an accessory mineral usually associated with 

quartz, plagioclase, and mica 0 Crystals as much as 2 inches in 

diameter were found at the Evans mine. Both flat and euhedral 

garnets are intergrown with muscovite at many mines, and with 

biotite at a few.

Beryl was seen in 61 of 131 pegmatites examined. Gem beryl 

was the principal product of three mines in Springfield, but 

most of the beryl is of the common green variety. Beryl encountered in feldspar or mica mining is often set aside and sold for 

$>30-$35 per ton, but the relatively small quantities of byproduct beryl obtained do not go fa* to defray mining C03tS 8 HltCtlv/ cock -' describes a beryl crystal weighing 2,900 pounds, and 

another calculated to weigh 2% tons, at the Alger mine. Beryl 

occurs most commonly as hexagonal crystals near the middles of 

pegmatites in quartz that may also contain crystals of potash 

feldspar. A beryl crystal several inches long was found in wall

7/ Hitchcock, C. H., op. cit., p. 515.
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 373

rock adjacent to a large pegmatite west of the French mine, but 

such an occurrence is unusual.

Apatite is most abundant at the Foss mine in Strafford 

County, where it is associated with cleavelandite, but it was 

also seen at about a fourth of the mines examined, generally 

associated with plagioclase, quartz, garnet, or other minor 

accessories. Hexagonal crystals of apatite that penetrate mica 

books commonly are oriented with the £ axes perpendicular to the 

cleavage of the mica, indicating a crystallographic relationship 

between the two minerals.

Spodumene, triphylite or lithiophilite, and a little lepidolite were seen in about a dozen pegmatites, associated with 

cleavelandite.

Roughly three-fourths of the pegmatites examined contain 

tourmaline. It is most plentiful (1) in quartzose parts of pegmatites, (2) associated with cleavelandite, (3) near contacts, 

either in pegmatite or wall rock. Blue and green varieties were 

seen in two pegmatites that also contain cleavelandite and lithium minerals, "but all the tourmaline seen elsewhere is black. 

Black needles are abundant in wall rock adjacent, to tourmalinebearing pegmatites, particularly in quartz-mica and sillimanitemica schist. Crystals of black tourmaline in the pegmatite at 

the Baer mine are as much as 10 inches in diameter.

Minor quantities of sulfide minerals, including pyrrhotite, 

pyrite, a: enopyrite or lollingite, molybdenite, and chalcopyrite, are enclosed ii ne quartz of the pegmatites. Typical 

examples may be « south of C^ - Hill quarry in a pegmatite 

composed almost t.. ..-ely of me° c'ive quartz.

Mineral zones an> eakg

As a general rule, the value of a pegmatioB depenc large 

part on the degree to which its valuable minerals are segregated. 

Pegmatites composed of the feldspar-quartz intergrowth graphic
374 STRATEGIC MINERALS INVESTIGATIONS, 1941

granite, of which there are many, cannot be mined profitably 

apart from certain zones, streaks, or pockets rich in feldspar 

or mica. Pegmatites less than 6 feet thick are mined from wall 

to wall, but a large pegmatite, that is minable for its entire 

width, such as the one in the French mine (see fig. 45), is 

exceptional.

Many of the large pegmatites (over 25 feet thick) that have 

been mined for mica are zoned as follows: (1) The pegmatite 

within a foot or two of the walls is composed of quartz, plagioclase, muscovite, and occasionally tourmaline, and most of the 

mica books are oriented with their cleavage perpendicular to the 

contacts. (2) Inward-from this contact zone there is a zone 

several feet thick composed of the same minerals in larger 

grains, from which large mica books are mined. (3) Between the 

mica zone and the center, the pegmatite consists mainly of 

intergrown quartz and feldspar, which in places contains strips 

of blotite. (4) The central part consists of discontinuous 

quartz masses, which are commonly lenticular and similar in 

attitude to the enclosing pegmatite. Some of these masses contain crystals of potash feldspar and beryl. Typical thinner

pegmatites also liave quartzose centers, with, marginal zones of 

plagloclase, quartz, microcline, and mica.

The minerals of some pegmatites, instead of being zoned in 

the manner described, are concentrated in streaks or zones several feet thick, generally parallel to the long sides of the 

pegmatite, but not systematic in arrangement, Streaks rich in

biotite, muscovite, cleavelandite, tourmaline, or apatite are 

common.

MICA 

Localization

Muscovite is distributed sporadically in most pegmatites, 

but minable bodies are localized in zones, streaks, or pockets,
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 375

in which the amount of recoverable mica ranges from 2 to 10 percent of the rock, and averages about 4 percent. The mica in 

most rich streaks is associated with quartz and plagioclase 

rather than with potash feldspar, and almost never with graphic 

granite.

The principal modes of occurrence of commercial mica are 

listed below. Further notes on the occurrence and character of 

mica in 131 pegmatites are included in table 8, at the end of 

this report.

(1) In quartz-plagioclase-muscovite zones in large pegmatites, near contacts with walls or Inclusions. Pegmatite consisting of quartz, plagioclase, and muscovite is typically finegrained within 1 or 2 feet of the walls, in a zone in which 

small mica books are oriented with their cleavage perpendicular 

to the contact. Prom 2 to 10 feet from the contact, however, 

there are large mica books in rock of approximately the same 

composition but of larger grain size. Such mica-rich zones may 

lie along either or both walls. Mica is also localized along 

the lower margins or sides of inclusions or pendants in some 

large pegmatites, such as those at the Keyes and Strain mines 

(fig. 42).

(2) In thin pegmatites and offshoots from large crosscutting pegmatites, generally conformable to their wall rocks 

and from 6 to 15 feet thick. Such offshoots commonly contain a 

higher proportion of plagioclase than the larger masses, but 

like them are generally more quartzose near their centers. In 

some, mica books occur throughout the entire thickness; in 

others, they are more abundant near the walls.

(3) Marginal to large masses of quartz, 2 to 15 feet thick, 

generally in the central parts of pegmatites. Mica occurs within some of the quartz masses, but more commonly it is found in 

quartz-feldspar pegmatite adjacent to them. Such concentrations 

of mica near quartz are seXLdom continuous for very great

442183 0-42-3
376 STRATEGIC MINERALS INVESTIGATIONS, 1941

distances» Large quartz masses are numerous in pegmatite outcrops, but mica is associated with relatively few. Aggregates 

composed almost entirely of small green wedge-shaped books less 

than 2 inches in diameter, with subordinate plagioclase, tourmaline, or garnet, occur in a number of the larger, pegmatites. 

Such an aggregate, 12 feet thick and 20 feet long, at the Ruggles mine is apparently associated with a large mass of quartz 

that contains blocks of potash feldspar. This and other masses 

of similar character seem to be related to massive quartz bodies 

near the centers of pegmatites.

(4) In more or less tabular mica-rich zones or streaks within pegmatites such as those at the Ruby and Palermo mines 

(fig, 40). Where mined they are 3 to 15 feet thick, and are 

composed mostly of quartz, plagioclase, and mica, with minor 

amounts of tourmaline, apatite, garnet, and other accessory minerals.

Physical properties and uses

Muscovite, the principal mica of commerce, has the approximate formula K(Al,Fe) 2 (Al,Si) 40 10 (OH,F) 2 . It crystallizes in

the monoclinlc system as six-sided crystals with prominent basal 

cleavage. Very few of the books mined, however, are euhedral

crystals. The perfect cleavage of muscovite and its physical

8/ properties determine its uses in industry and its value o-^ The

combination of a number of peculiar physical properties makes

mica essential for certain electrical uses, The principal physical properties have been described and illustrated by ster9/

rett, and the following are the more important in determining

the value of mica and its uses.

 &/ For uses of mica, see fflerum, H. P., and others, Ike mica iniusiryj 

U. S. Tariff Commission. Kept. 130, 2d ser., pp. 11-26, 193&. 

2/ Sterrett, D. B., op. cit., pp. 11-18, pis. 3-g.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 377

Staining. Clear domestic mica contains no inclusions of 

iron oxide or other substances. That which contains inclusions 

(principally iron oxide) is specked or stained, and is used 

mainly in electrical appliances that do not demand the best 

grades. The specks are distributed at random through some 

sheets, but in others magnetite or hematite inclusions are crystallographically arranged parallel to the ""lines of the percussion figure. "Spotted," "black-stained," "powder-specked," 

"electric," and "black" mica are other terms used to denote 

iron-oxide staining.

Mica is said to be clay-stained if fine particles of clay 

have been introduced between the sheets. Such staining is relatively rare in New Hampshire because the pegmatites have been 

weathered only to a shallow depth.

Air and water bubbles between sheets, if they are few, can 

be removed by careful splitting, but if abundant .they reduce the 

value of the mica.

Flexibility. In the manufacture of airplane spark plugs, 

films of "cigarette" mica, not over twelve ten-thousandths of an 

inch thick, are wrapped around a rodlike spindle, and they must 

be flexible enough to be rolled into a cylinder a little more 

than an eighth of an inch in diameter without cracking. Mica 

for this purpose must not only be highly flexible, but must have 

flat cleavage faces and be free from inclusions and other imperfections.

Cleavage. Perfect cleavage is one of the most Important of 

mica's valuable properties. To be suitable for the most' exacting uses, mica must split easily into perfectly flat sheets of 

uniform thickness throughout. Wavy or curved cleavage surfaces 

generally result from distortion of the mica crystal. Other 

cleavage irregularities, such as "A" wedge and herringbone 

structures, apparently originated at the time of crystallization

10/ ffierum, H. P., and others, op. clt., p. 19.
378 STRATEGIC MINERALS INVESTIGATIONS, 1941

of the mica, presumably forming tinder slightly different conditions from the flat books. "A" mica has two sets of cleavage 

imperfections, called ridges or reeves, which intersect at an 

angle near 60°, forming an Ao "A" mica is present in different 

amounts in nearly every pegmatite, but the best mines contain 

relatively little. Books of "A" mica that are thicker at one 

end than at the other are called wedge mica. Wedge mica is 

relatively uncommon in New Hampshire, but at several mines, such 

as the one at Chandler Station in Newport, it constitutes practically the entire output Plat sheets can be trimmed from the 

centers of some "A" books, but as a general rule a high proportion of "A" mica means a high proportion of scrap.

Herringbone mica differs from "A" in having three sets of 

reeves, two of them intersecting a central splnelike set at 

angles of about 60°. Herringbone mica does not split easily and 

is called tanglesheet. Some books grade from herringbone on one 

side to flat, easily splitting sheets on the other. Most muscovite that is intergrown with biotite is tanglesheet or has

herringbone structure. Sheets that are difficult to split because of random fine cracks are said to be haircracked.

Another cleavage imperreotion, known as ruling, apparently 

results from deformation of the mica book. Some books that are 

otherwise of large size are ruled to such an extent that they 

are worthless except as scrap. Since ruled, crumpled, and wavy

mica is most abundant near faults, the test mica mines are in

pegmatites that have not "been, aoronnea..

Intergrowths with other minerals, Intergrowths of other 

minerals lower the value of a mica t)00k. Sheets Of biotite ana

mUSCOVite COinmonly form parallel Intergrowths. Flat to-u.nnaia.no

needles ana garnet, toth. fiat ana euhedrai, also occur between 

sheets of muscovite; and apatite, quartz, and albite are also 

commonly Intergrown with muscovite. Plat tourmaline and garnet 

at the Island mine are more abundant in "A" mica than in flat.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 379

Color, The terms most commonly used to describe color are 

ruby, rum, green, white, and brown. Ruby and rum micas are the 

most desirable because they are usually slightly better than the 

green and brown in respect to certain electrical properties such 

as power factor. Mica from about 60 percent of the mines was 

classified in the field as light rum, and the color of much of 

the New Hampshire mica is notably uniform 0 Ruby mica occurs at 

a number of mines, and there are gradations between it and the 

light rum. Other colors that occur less, commonly In New Hampshire are light yellowish green, greenish white, dark greenish 

rum, and other shades of rum and green.

The color of mica from a given pegmatite is relatively constant. Exceptionally, two or more colors may be reported from 

different parts of the same pegmatite. At the French mine (see 

fig. 45), most of the product was stained light-rum mica, but 

ruby and light green were also found.

Variations in the color of muscovite doubtless reflect a 

variation in composition. Green muscovite probably contains 

more Iron than ruby. Most mica that is stained by iron-oxide 

inclusions is green rather than ruby. Muscovite closely associated with Iron-rich biotite is generally of a ruby or rum color 

(less iron); where biotite is scarce or absent, the muscovite 

tends to be green or stained (more iron). Although this is not 

an invariable rule, it Indicates a relationship between iron 

content and color.

Mica that occurs with cleavelandite and lithium minerals is 

almost invariably light yellowish green and may be either clear 

or stained.

In some mica books ruby- and rum-colored zones alternate 

from the center out to the edges of the cleavage plates.

Dielectric constant. The simplest expression of the dielectric constant of mica Is the ratio of stored energy in a dielectric field occupied by the mineral to the stored energy that
380 STRATEGIC MINERALS INVESTIGATIONS, 1941

would exist in the same space if air were used in place of

ll/ mica. The dielectric constant of most mica ranges from 6.5 to

8,5 averaging about 7.2. Staining and color of mica seem to 

have little effect on its dielectric constant. In determining 

the suitability of mica for condensers, the dielectric constant 

need not be considered, because mica that is otherwise suitable 

for this purpose always has a sufficiently high dielectric constant.

Power factor. The power factor of a substance, expressed in 

percent, is a measure of the loss of electrical energy in a condenser in which that substance forms the dielectric medium. 

Since excessive power loss results in overheating and destruction of the condenser, mica of low power factor is essential. 

Mica with a power factor greater than 0.04 percent is seldom 

used for condensers.

To determine the approximate suitability of New Hampshire 

mica with regard to the important property of power factor, 

carefully selected samples representing 65 mines were split into 

films 1 to 4 mils thick and submitted to the National Bureau of 

Standards. The tests of power factor were made by E. L. Hall. 

A part of the explanatory section of his report follows:

The power factor was measured at room temperature at a frequency Of 1,000 kilocycles per second. A small electrical condenser was prepared from each sample using two small pieces of 

lead foil attached on opposite sides of the mica specimen * # #. 

The power factor tests were made using a type" 513-C radio-frequency bridge made by General Radio Company, Cambridge, Massachusetts. The standard in terms of which the measurements were 

made, was a General Radio type 722-N precision variable air condenser.

The results of these tests indicate a low power factor for 

almost all of the samples. Of the 76 New Hampshire mica specimens tested, 33 of the measurements were 0.01 percent, 33 were 

0.02 percent, 6 were 0.03 percent, 3 were 0.04 percent, and one 

was 0.09 percent. The specimens were carefully selected so that 

the results are not representative' of the total output of the

ll/ Wierum, H. P., op. cit., p. 22.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 381

respective mines. They indicate, however, that by proper selection mica of low power factor is obtainable from many mines. 

The following is a list of mines from which samples were tested, 

together with mine numbers (as shown on pis. 62 and 63, and 

table 8) and power factors of the specimens:

Table 5. Power factors of New Hampshire muscovite 

[Tests made by the National Bureau of Standards]

Mine

A f* "pi r*n n -

Akerman prospect. ........

A T CTAT* - . * »

Alstead...

Bailey. . .......

Bennett Bros. . . 

Beryl Mountain. 

Blgo...........

Carpenter,

T?7iQv^T/>

Colby. .........

Cole ...........

Columbian Gem 

Co...........

T^Q YiVn 1 T* V

Tin nVinT'TT'

Davis, Charles. 

Diamond Ledge . .

T?l o "1" r» Vi o T*

Ford, Harry. . . .

Globe. .........

Hale, ..........

Hoyt Hill......

Hut chins Hill..

T a T a r\r\

Kilton..o......

TTo T* Q t* r\Y\

Mo Y» Q 4* r\Y\

McGinnis , 

Whicher, and 

Pillsbury

Mine 

No.

45

25

58

97

 zp

64 

89 

110

53

68

72

61

75

35

35

16 

14 

62

fi?

o

42

47

73

63

70

10

48

30 

122

IIP

40

57

P4.

?4

9

115

Power 

factor 

(percent)

0.02

.02

oOl

.01

.02

.02 

.04 

.02

.01

.02

.02

.02

.02

o?

.01

.02 

.01 

.01

.02

.01

.01

.02 

.09

.02

.02

.01

.02

.01

.01

.02 

.02

.02

.01

.01r\"i

.02

.02

.01

Mine

Prescott Hill.. 

Price. .........

Price. .........

Rice. ..........

Rice. ...........

Roby. ..........

Ruby. ..........

Ruby. ..........

Ruggles. .......

Ruggles New 

Hill.........

Standard 

(Belden).

Standard (in 

Alexandria) . . 

Strain.. .......

Strain. ........

Straw. .........

Trow Hill......

United. ........

Vo "1 An r* 1 n

West Rumney. . . . 

White, Jehial.. 

Whitehall......

Whitehall on 

Braley Hill.. 

Wilmot .........

No name, in

No name, in 

Graf ton.

Mine 

No.

126

19

19

19

26

74

17

81

65 

128

128

76

?0

20

 17

51

51

56

56

54

44

28

43

43

52

36

85

?Q

7

69

1

5 

124 

, 50

33 

82

111

60

Power 

factor 

(percent)

0.03

.01

.04

.02

.02

OP

.01

.01

.01 

.03

.03

.01

.02

.01

.01

.01

.03

.03

.04

.01

.01

.02 

.01

.01

.02

.01

.02

.02

.01

.02

.02

.02 

.01 

.02

.01 

.01

.01

.01
382 STRATEGIC MINERALS INVESTIGATIONS, 1941

Other tests made by the National Bureau of Standards demonstrate the effect of air bubbles on power factor. The tests 

were performed on a thick piece of mica from the Frank Carpenter 

mine (No. 68) The results are quoted:

The piece first tested, designated A, had a thickness of 

20 mils. Two large bubbles or pockets were observed within the 

mica and under the lead foil electrodes. The power factor was 

0.05 percent.

Piece B, 2 mils thick, was split from A, a new electrode 

attached under that first placed on A and the power factor measured as 0.02 percent. No bubbles were present.

The thick piece remaining, (A minus B), 18 mils thick, was 

measured and a power factor of 0.09 percent obtained. The bubbles previously mentioned were in this splitting of mica,,

Another piece C, 4 mils thick was split off which contained 

the bubbles. The power factor was 0 0 06 percent.

The thick piece then remaining, without visible bubbles, 14 

mils thick, was measured and found to be 0.005 percent.

A piece about 9 mils thick was split off, measured, and a 

power factor of 0.005 percent obtained.

The remaining piece, about 5 mils thick, was measured and a 

power factor of 0.01 percent obtained.

These tests were all made transversely through the same mica, 

some sections appearing in several of the tests. It is evident 

from these results that the presence of bubbles between the 

electrodes increased the power factor.

Sheet mica sizes and prices

New Hampshire mica that is not mined by consuming companies 

is generally sold to buyers as scrap or as mine-run mica and is

bought by the ton. The price for scrap mica is fairly uniform, 

ranging from $15 to $2O per ton. The "buyers grade and classify 

mine-run mica according to their own uses. The price for minerun mica ranges from $40 to more than $100 per ton, depending 

upon (1) the economic condition of the mica industry, (2) the

quality of the sheet mica, and (3) the proportion of the larger 

sizes in the mine run. The mica produced at most mines is 65 to 

95 percent scrap. At the best mines the average is about 75 

percent. The remainder is about 25 percent sheet and 75 percent 

punch.

mica, Punch mica in the domestic classification in-
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 383

smaller than 2 by 2 inches but larger than a circle 1-|- inches in 

diametero Prices for punch mica range from 5 to 15 cents per 

pound.

Sheet mica. Table 6 shows the various sizes into which 

clear sheet mica is graded according to the domestic classification, their price ranges, and the approximate percentage of each 

size that might be obtained from a good mine. The proportions 

of these sizes, however, are by no means constant throughout1 a 

given pegmatite, and vary considerably in different mines. Some 

mines are well known for the large sizes that they produce; 

others yield nothing larger than 4 by 6 inches.

Table 6. Size distribution and price ranges 

of trimmed domestic sheet mica

Ti T

2 x

2 x

3 x

3 x

3 x

4 x

6 x

R x

Size 

( inches )

2.................

2.................

3.................

3.................

4.................

5.................

6.................

8.................

10...... 0..........

Probable proportion of total 

(percent)

25

22

22

10

7.5

8

5

.1

100.0

Price range 

per pound

$0.15-$0.60

.30- 1.00

.45- 1.40

.60- 2.00

.80- 2.30

1.00- 2.65

1.75- 3.60

2.25- 7.00

3.50-11.00

Fast production

Commercial production of mica in the United States began in 

1803, at the Ruggles mine, Grafton County, No H. New Hampshire 

furnished all the mica used in the United States prior to 1868, 

when production began in other states, and has been a major 

producer every year since that time. Total production of sheet 

and punch mica in New Hampshire during the period 1908-39 is 

shown in table 7. Most of this production has come from a few

relatively large mines. Of the total of 11,457,271 pounds pro12/ 

duced since 1917, nearly half was obtained from the French, 

12/ The mines are numbered in table g and are designated by corresponding numbers on plates 6? and 63.
384 STRATEGIC MINERALS INVESTIGATIONS, 1941

Alexandria, and Wilnot mines. The Alexandria mine produced

4,031,067 pounds of mine-run mica (including scrap) during the

13/

years 1917-31, an average of 268,738 pounds per year. Most of

the remainder during the period 1917-39 was produced by the following 10 mines: Valencia, Standard, Nichols, Ruby, Alstead, 

Palermo, Danbury, Big, Strain, and Ruggles. Approximately 30 

other mines- produced smaller quantities of mica between 1917 and 

1939.

Table 7. Production of sheet and punch mica 

in New Hampshire, 1908-39 I/

Year

1908

1908

1910

1911

1912

1913

1914

1915

1916

1917

1918

1919

1920

1921

1922

1923

Pounds

12,000

55,808

117,170

289,473

308,047

731,478

133,556

96,685

125,502

472,519

376,900

235,724

284,862

491,743

475,647

835,751

Value

$1,200

12,086

26,109

35,103

32,238

65,765

39,588

59,414

64,386

159,822

106,200

90,915

83,811

63,249

63,240

107,674

Year

1924

1925

1926

1927

1928

1929

1930

1931

1932

1933

1934

1935

1936

1937

1938

1939

Pounds

744,133

1,120,857

1,371,890

720,219

774,143

984,778

673,064

441,164

146,014

167,464

161,430

131,586

285,822

235,055

2/282,836

43,670

Value

$88,737

198,858

235,890

78,849

63,470

82,657

53,304

36,368

17,978

22,008

14,423

13,727

22, -920

20,119

49,254

3,738

I/ Minerals Yearbook, 19^0, p. lU05. 

£/ Connecticut included.

The history of mining since 1803 provides many examples of 

mines that operated intermittently. Such, records of alternate 

periods of operation and idleness indicate that at least a few 

of the mines now idle could be reopened, although their average 

rate of production might be lower than the average of the past.

The Rice mine, reopened on October 18, 1940, produced 184 000

I4/ 

pounds of mine-run mica by May 31, 1941. The many prospects

13/ Published by permission of the General Electric Co.

W/ Published by permission of L. F. Crowe, General Electric Co.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 385

and it is reasonable to suppose that some of them would develop 

into new mines with further prospecting.

Cost of mining

157 

Mining costs at the French mine in 1923 and 1924 averaged

only $82 per ton of mine-run mica produced. Although this figure is below average, several operators expressed the opinion 

that very few mines can be operated profitably if the value of 

their mine-run mica is less than $100 per ton. As an example, 

mine-run mica would be worth $100 per ton if it comprised 80 

percent scrap ($20 per ton), 15 percent punch ($0.10 per pound), 

and 5 percent sheet ($0.54 per pound). If the total production 

of a mine is assumed to be scrap mica, valued at $20 per ton, 

recoverable mica must constitute 12|- percent of the rock if the 

total value of rock mined is to be $2.50 per ton. Only exceptionally, in rich pockets, does mica constitute 12^- percent of 

the pegmatite. The quantity of mica in the rock mined commonly 

ranges from 2 to 10 percent, of which from 65 to 95 percent is 

scrap. No New Hampshire pegmatite, therefore, can be mined 

solely for scrap. If, on the other hand, the mine run contains 

sheet and punch mica enough to raise its value to $100 per ton, 

recoverable mica need only constitute 2-g percent of the rock 

mined to make the tenor of the ore $2.50 per ton. The $100 

mininum, however, is perhaps not to be regarded as 'absolute, for 

costs of mining depend upon a number of variable factors, being 

by no means constant in different parts of an individual mine.

Possible future production

The low power factor of much New Hampshire mica is indicated 

by the tests made at the National Bureau of Standards. Since 

properties other than power factor are also important in

According to records furnished by Paul French, Eugene Munsell & Co., 

Hew York.
386 STRATEGIC MINERALS INVESTIGATIONS, 1941

evaluating mica, the proportion of New Hampshire mica that would 

be of condenser quality can only be conjectured. The proportion 

of Indian mica that is classified as fair-stained or better 

(potentially of condenser quality) probably never exceeds 10 

percent of the total sheet mica, and a good part of this is discarded in the process of splitting. Mica of condenser grade 

probably comprises no more than a few percent of the total sheet 

mica produced by a mine. Much of the New Hampshire mica is flat 

and splits easily 0 The cost of labor necessary to split and 

carefully grade mica has precluded the production of condenser 

films from New Hampshire mica in the past, but mica of the required quality doubtless occurs in the State.

The New Hampshire pegmatites are not depleted, and they 

should produce mica during the next several years at about the 

same rate as in the past. No closer estimate of future production seems possible because, from the nature of the deposits, 

none contain blocked-out reserves of ore.

The reserves of individual deposits cannot be estimated even 

approximately owing to the erratic distribution of mica within 

pegmatites. Although mica-bearing zones in some pegmatites have 

persisted for hundreds of feet, there is no assurance, in an undeveloped pegmatite, that they will do so; in mica mining there 

is .no blocked-out ore. It is possible to sample qualitatively, 

but not quantitatively,, Core drilling of pegmatites for feldspar has been attempted, but its value as a guide to mica mining 

is doubtful. Drilling could be used to locate pegmatite if 

there were reason to believe that thin pegmatites if present 

might bear mica, but it would not necessarily disclose the size 

or quantity of mica books. In the final analysis, prospecting 

and mining merge into one uncertain venture, and the actual 

value of any single deposit is determined by results.

The average annual production of sheet and punch mica in 

New Hampshire during the period 1908-39 was 416,470 pounds.
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 387

Production during the years 1931 to 1939, however, averaged only 

210,000 pounds per year, and that in 1939 was only 43,670 pounds. 

The years"of small production indicate severe competition from 

foreign sources of supply, not depletion of reserves. Recorded 

production of 96,685 pounds in 1915 has been exceeded every subsequent year except 1939.

From average annual production of 416,470 pounds of sheet 

and punch mica over a 32-year period and unpublished production 

figures from many mines, it is estimated that, at a slightly 

higher cost than the average of the past, a production of at 

least 500,000 pounds of sheet and punch mica could be maintained 

for a period of several years, of which between 100,000 and 

125,000 pounds would be sheet. An annual production of 

1,000,000 pounds or more of sheet and punch might be attained by 

more intensive mining.

MINES

Although many mines operated for feldspar or for mica produce the other as a byproduct, commercial potash feldspar and 

sheet mica generally occur in different parts of the pegmatite, 

so that every mine may be classified as a feldspar mine or as a 

mica mine. Byproduct mica from feldspar mining is largely scrap. 

Of 131 mines examined, mica is the principal product in 84 and 

feldspar in 47. Of 85 mines in the Grafton district, 67 are 

dominantly mlca 8 Of 45 in the Keene district, 16 are dominantly 

mica. Six feldspar mines and prospects and 2 mica mines were in 

operation during the fall of 1940.

Most mica mines are operated as open pits or quarries, 

although mica-rich zones have been followed underground at some 

of the larger mines. The mines are caved in the decomposed pegmatites at the Standard (in Alexandria), African, and Alexandria, 

but mines elsewhere are open because most pegmatites are hard, 

resistant, and relatively unweathered. The Palermo mine
388 STRATEGIC MINERALS INVESTIGATIONS, 1941

(see fig. 40) is said to extend at least 300 feet down a 45° 

incline. The workings at the Ruggles mica-feldspar mine are 

more than 800 feet long.. The Big feldspar cut (see fig. 44) in 

Alstead is nearly 200 feet across, and is said to have been more 

than 200 feet deep before the southeast wall caved. The French 

open cut (see fig. 45) is 125 feet deep and 700 feet long. 

Unless the pegmatite is less than about 8 feet thick, only the 

richest part is removed in mining. The attempt at the Standard 

(Belden) mine (see fig. 43), in Orange, to quarry the entire 

mass of a large pegmatite for mica proved costly, and subsequent 

operations have been confined to parts of pegmatites in which 

mica is localized.

The largest mines have been operated by companies, most of 

which are consumers as well as producers, that employ 8 to 30 

miners each, but a few small mines or prospects are operated by 

2 or 3 men each. Companies that consume their own product 

classify it according to their uses, and information as to relative proportions of various sizes of sheet mica in the mine run 

is therefore scarce.

On the following list (table 8) the mine numbers correspond 

to those showing the location of the mines on plates 62 and 63. 

The product mica is indicated by M, feldspar by P.

Table 8. New Hampshire mica and feldspar mines,

with notes on the character and occurrence Of ttlC mica

No.

i

2

TS. o

4

Name

Valencia. . . ..

Fie toner.

Beldem . . . ..

Product

nr

M

M

M

Character

of mica

Light rum. . .

Rum, nearly

ruby.

Light green.

Little seen.

Notes on occurrence 

of mica

(M in piagioclase zone

flbOUt/ i ft, belOW hanglng waii; (2) elsewhere

in large pegmatite,

principally near quartz

-bociioa. (gee fig. 39o)

ASSOCiateCl With quartz in

pegmatite 8-15 ft.

thick, mostly near

hanging wall.

In large pegmatite.

Beneath quartz mass in

large irregular pegmatlte.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 389

^Quartz dump

Basaltic dike

Incline 15'deep

Inclines down dip to 

east from open cut 

are now caved

100 Feet

EXPLANATION

Pegmatite

Hanging wall, showing dip

T-t-r-r

Pit

SiMimanite-mica schist

/S ts 

Strike and di'p of foliation

 ''/, ,»'

Dump

Figure 39. Sketch nap of the Valencia mine.
390 STRATEGIC MINERALS INVESTIGATIONS, 1941

Table 8. New Hampshire mica and feldspar mines Continued

No.

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

?("]

21

Name

West Rumney

(Atwood,

Burley) .

J. W. Burley.

McGinnis,

Whlcher,

and Pillsbury.

On Streeter

Mount ain e

Prank Davis. .

Newt Kinney. .

Diamond Ledge

Pennsylvania

Coal & Iron

Co.

Charles Davis

Mica Products

CO..

Palermo

(Hartford).

Pike Ledge...

Product

M

P

M

MF

M

M

M

M

M

M

F

M

M

M

MF

n

M

Character 

of mica

Light rum,

nearly ruby.

Light rum. . .

Light rum. . .

Light rum;

mostly

scrap.

Light rum;

small.

Light rum;

small o

Little seen.

Light rum;

scarce.

Light green;

mostly

scrap.

Light rum. . .

Light rum...

Slightly

stained;

ruby.

Light rum,

nearly ru-

"by 

Light rum,

nearly ru. 

ty.

Light rum,

ruby, and

yellow

green.

Light rum

and ruby.

Light rum;

tanglesheet.

Notes on occurrence 

of mica

In pegmatite 4-20 ft.

thick, mostly with

quartz and plagioclase

near hanging wall.

Feldspar mine. Pegmatite

more than 50 ft. thick.

Entire thickness of 10-18

ft. removed.

Beneath a quartz body 10

ft» thick in a pegmatite more than 50 ft.

thick.

Near contacts of quartzose pegmatite 10 ft»

thick.

Near contacts in quartzose pegmatite 12 ft. or

less thicko

Near hanging wall of

large pegmatite; another pegmatite 500 ft.

south of mine was prospected, and. contains a

little greenish-rum

mica.

Near quartz body 5 ft.

thick, 30 ft, below

hanging wall.

Near quartz body 3-5 ft.

thick, 25 ft. above

footwall of large pegmatite.

Feldspar mine. Mica intergrown with biotite

and relatively scarce.

Mostly near walls of a

pegmatite 8-15 ft.

thick.

Pegmatite 4-8 ft. thick,

entire thickness remo-v-©cLo

In pegmatite 8-16 ft.

thick, mostly near center,,

Tabular quartz-plagioclase-ipuscovite zone in

central part of large

pegmatite. (See fig.

40. )

4 openings, on pegmatites

6-18 ft. thick that may tie orrsnoots rrom a

larger pegmatite to the

south.

In large pegmatite, with

quartz, microcline and

graphic granite.
GEOLOGICAL SURVEY 

72° 5' 72°00' 7I°55' 7I°5O

BULLETIN !H1 I'KATK tti

/I "45'

Numbers refer to mine numbers 

given in tables in the text

72°5' 72°00' 7l°55' 7I°5O'

MAP SHOWING LOCATIONS OF MICA AND FELDSPAR MINES OF THE GRAFTON DISTRICT, NEW HAMPSHIRE

I 0 5 Miles

U. S. GOVERNMENT PRINTING OFFICE : 1941-O 442183 O - 42 (Faces p. 390)
GEOLOGICAL SURVEY BULLETIN 931 PLATE 63

72°20' 72°I5'

Numbers refer to mine numbers 

given in tables in the text

72°20' 72° 15' 

MAP SHOWING LOCATIONS OF MICA AND FELDSPAR MINES 

OF THE KEENE DISTRICT, NEW HAMPSHIRE

I o 5 Miles

U. S. GOVERNMENT PRINTING OFFICE : I 94Z-O 442183 O - 42 (Faces p. 390)
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 391

EXPLANATION

Sillimflnita-mica schist

Strike and dip of schist

Dip of contact

Approximate outline of 

main incline stopea 

(From O.B.Sterrett, 

^>\ Geological Survey 

a, Bulletin 7*o,/o./3/)

Figure 40. Plan of the Palermo mine. 

Table 8. New Hampshire mica and feldspar mines Continued

No.

9?

23

Name

man) . 

Hobart Hill 

(Hayes).

Product

PM

M

Character 

of mica

Yellow 

green; 

small .

Notes on occurrence 

of mica

With quartz, cleavelandite, beryl, and tourmaline in pocket near 

middle of pegmatite 60 

ft. thick.
392 STRATEGIC MINERALS INVESTIGATIONS, 1941

Table 8 0 New Hampshire mica and feldspar mines Continued

No.

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

59

Name

Marston (East

Branch) .

Akerman prospect.

Truman Patten

Monarch ( and

Tasker).

Standard ( in

Alexandria).

Eugene Tucker

Hutchins Hill

(New Haven

Mica Co. ).

Alexandria

(Mud).

Whitehall (on

Braley

Hill).

Roby (Wild

Meadows ) »

Rousseau

prospect.

Kimball Hill

(India Mica

Co.).

Product

MF

M

M

M

M

M

M

M

M

PM

M

M

n

M

M

M

Character 

of mica

Light rum,

nearly rubyLight rum,

some

stained.

Light rum o.o

Light rum. e .

Light rum. . .

Light green

and ruby;

mottled;

herringbone o

Light green

or white;

some

specked.

Light rum. . .

Greenish rum

Light rum. o

Light green

or white;

specked.

Ruls T 5 s ome

stained.

Light rum.io

Light rum;

scarce*

Light Wffl...

Notes on occurrence 

of mica

Probably associated with

quartz in pegmatites

10-15 ft. thick.

Near quartz bodies 2 ft.

or less thick on pegmatite outcrop 20 ft.

wide.

Near quartz bodies 2 ft«

thick, at center of

pegmatite 70 ft. thick.

Mine inaccessible.

3-15 ft. below hanging

wall of thick pegmatite.

With quartz and plagioclase, near hanging

wall of pegmatite 10-12

ft. thick.

With quartz, microcline,

and beryl in zone 6 ft.

thick in middle of pegmatite 25 ft. thick.

'in zone 4-10 ft. thick

along northwest wall of

pegmatite 30-50 ft.

thick.

On west side of quartz

mass 6 ft. thick in

pegmatite more than 40

ft. thick.

In gray quartz bodies in

large pegmatite that is

mostly graphic granite.

Pegmatite. 6-8 ft. thick.

With quartz and microcline in zone 8-10 ft.

thick, separated from

hanging wall by 2-4 ft.

of fine-grained pegmatite. (See fig. 41.)

Ttlin pegmatite consisting

mostly of quartz, plagi<^ole».s 0 j eLndl small

 muscovite.

Best mica said to occur

with quartz and plagioClaae in center or pegmatite 15 ft. thick;

darker A mica nearhanging wall.

Scattered prospect holes

on pegmatite outcrop 40

ft. wide. witn quartz ana piagio»

clase, between discontinuous central quartz

bodies and fine-grained

pegmatite along contacts of pegmatite 6-18

ft. thick.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 393

Pegmatite can be traced 

northward at least 700 '

N

hickquartz mass

Water filled incline 

15 feet deep

EXPLANATION

Pegmati-te Porphyritic biotite gneiss

Hanging wall showing dip Strike and dip of foliation

Pit Dump 

Figure 41. Sketch nap of the Danbury mine.
394 STRATEGIC MINERALS INVESTIGATIONS, 1941

Principal cut for mica 

\\ 

11=

,, "

Bottom of inclusion or 

pendant,pitch 3S°N,

Grooved fault surface

EXPLANATION \\\ 

II

Dump 

S*75°

Strike and dipoffoliation

Strike of vertical 

-foliation

50 50

Figure U2. Sketch map of the Strain mine.
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 395

Table 8. New Hampshire mica and feldspar mines Continued

No.

40

41

42

43

44

45

46

47

48

49

50

51

52

Name

Smith Pasture

(Wilkins).

Harry Ford

(McConnell)

Strain (Star,

Sanborn) 

Standard

(Belden).

°

African

(Fellows).

Baer (Hob art)

Hoyt Hill....

'

Summit Mica

& Mining

Co.

Whitehall....

Ruby (and

Barney ) 0

Straw. o . . . . . o

Product

M

F

M

M

M

M

M

M

M

M

F

MF

M

Character 

of mica

Light rum. . .

Light rum;

scarce 0

Yellow green

Light rum

or white.

Light rum. . 

Ruby; mostly

scrap.

Yellow green

Light green.

Ruby, some

stained.

Light rum;

scarce.

Light rum;

scarce.

Light rum

and ruby.

Rum, small..

Notes on occurrence 

of mica

(1) Near inclusions in

pegmatite; (2) near or

in quartz masses 3 ft.

or more thick in pegmatite over 40 ft. thick.

Feldspar prospects. A

little A mica associated with large quartz

bodies.

(1) In streaks with

quartz or cleavelandlte

enclosed in finergrained parts of the

pegmatite; (2) near inclusions.

In offshoot 10-12 ft.

thick from large pegmatite 200 ft. across.

(See fig. 42.)

(1) Near or in quartz

masses in pegmatite at

least 50 ft. thick; (2)

associated with quartz

and cleavelandite. (See

fig. 43.)

Probably most abundant

near Inclusions in irregularly shaped pegmatite.

With quartz and cleavelandite in pegmatite,

not over 7 ft. thick,

that is probably an

offshoot from a thicker

body.

A33OCJ.&.T/6CL Wl tn. CJ.6Q.V6"

landite and tourmaline

in pegmatite 20-30 ft.

thick.

Pipellke pegmatite pitching north. Entire

thickness as well as

some wall rock removed

in mining.

On large pegmatite outcrop 40-150 ft. wide

and more than 500 ft.

long.

Feldspar prospect.

In tabular zone 10-15 ft.

thick of quartz, p.lagloclase, mica, apatite,

and a little microcline,

near middle of pegmatite at least 100 ft.

wide.

(1) Near walls; (2) with

microcline in or near

quartz mass 6 ft. thick.
396

Inclusion of tourmalinized 

mica schist;

N

25-'

Stope, under 

water

Pit

Dump

6'

Figures refer to elevations 

above water level

Figure ^3. Sketch map of the Standard (Belden) mine.

Table 8 0 New Hampshire mica and feldspar mines Continued

No.

53

Name

Boardman. . <>

Product

M

Character 

of mica

Light rum, 

near ruby.

Notes on occurrence 

of mica

At several places on pegmatite outcrop at least 

150 ft, wide.
 MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 397

Table 8.--New Hampshire mica and feldspar mines Continued

No.

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

Name

Ruggles New

Hill.

Whitehall,

on Isinglass Mountain,

Kilton.......

A T rp^Y1

No name, in

Grafton.

Evans (Eureka).

Glover o .... <>

Bennett Bros.

Prescott Hill

( Gage ) .

DeMott.o.....

Levering

prospect.

Frank Carpenter,,

Product

M

P

PM

M

MF

M

M

PM

PM

M

FM

F

M

M

M

Character 

of mica

Light yellow

green s

Light rum,

some

greenish.

Light rum. . 

Light rum,

slight ruby cast.

Light rum

and ruby;

some wedge

Light rum. . .

Light rum,

near ruby.

Light rum 0 . .

Light rum

and green

wedge .

Light rum

and ruby.

Light rum. . .

Light rum;

scarce.

Light rum» . .

Ruby, scarce

Ruby, some

stained.

Notes on occurrence 

of mica

With quartz and cleavelandite, mostly near

hanging wall of pegmatite 7 ft 0 or more

thick.

Mostly with plagioclase

in pegmatite 100 ft.

thick mined for feldspar.

Associated with" quartz

and plagioclase in zone

10-15 ft. thick near

contacts of large

cross cut ting pegmatite

that pitches south.

In zone 10-12 ft» thick

beneath flat-lying

hanging wall of large

pegmatite.

Wedge books common below

and in lower part of a

quartz mass 6 ft. thick.

Also in other parts of

the large pegmatite 

Pegmatite 2-12 ft. thick.

Mica scarce.

Mostly near contacts of

pegmatite 20 ft. thick.

Much intergrown»with biotite; pegmatite at

least 50 ft. thick.

Best mica is 1-5 ft. below hanging wall of

pegmatite 30 ft, thick.

With quartz and plagioclase in zone 4 ft.

thick near footwall of

pegmatite 35 ft. thick.

Mostly near quartz bodies

in pegmatite whose outcrop is at least 100 ft.

wide.

Feldspar mine. Mica said

to be richest near

footwall of Gage (east)

cut.

Near quartz masses several feet thick.

In quartz in pegmatite 15

ft, thick, enclosed in

granite.

In zone several feet

thick of quartz, plagioclase, mica, tourmaline, and apatite, near

middle of pegmatite

outcrop at least 100 ft.

wide.
398 STRATEGIC MINERALS INVESTIGATIONS, 1941

Table 8. New Hampshire mica and feldspar mines Continued

No.

69

70

71

72 

7?

74

75

76

77

7R

79 

80

81 

R2

83

84 

85

86

Name

Hale (Buckley).

Aaron Ledge 

(Lamb).

Colby (Randall. Joe 

Hill).

Columbian Gem

Co. *

Stewart Hill.

Bog Hill 

prospect. 

Currier prospect,

Powell. 

Wilmot.......

Elkins prospect,

Trow Hill....

Chandler Station,,

Product

M

M

M

/ 

M -

FM

Beryl

M 

Beryl

M 

Beryl

M

P

F

M 

M

FM 

MF

P

F 

M

M

Character 

of mica

Light rum. . 0

Light rum. . .

Light rum... 

Light rum

and light 

ruby. 

Ruby. .......

Ruby. .......

Light rum

and green, 

slightly 

stained.

Light rumj 

small ,, 

Light rum, 

some 

greenish

rum.

Light rum. . .

None seen 0 . .

Rum 0 .. .... oo 

Light rum. . .

Yellow green 

stained; 

mostly 

wedge, 

scrap.

Notes on occurrence 

of mica

quartz bodies near middle of pegmatite 8-20 

ft. thick; (2) near 

walls. 

In quartzose zone near

middle of pegmatite 

whose outcrop is at 

least 100 ft. wide. 

Scarce. Prospecting followed quartzose zones 

in large pegmatite outcrop as much as 250 ft. 

wide 0 

In irregular cross cut ting 

pegmatite.

Probably in quartzose

parts of large flatlying pegmatite. 

In pegmatite 3-15 ft.

thick that thickens 

southeastward from mine 

Little mica observed.

thick, poorly exposed.

"M-5 r» n Qr*OY*f*ft

Feldspar prospect.

Prosp.ect on large pegmatite outcrop.

Alongside a quartz mass 

15 f to. thick, near middle of "pegmatite 50 ft. 

thick, 

Most mica near walls of 

pegmatite 4-10 ft. 

thick, associated with 

plagioclase.

Muscovite. 

Mostly in quartz near 

middle of pegmatite 20- 

25 ft. thick, but also

in other parts. 

Pegmatite is 40 ft. thick 

at top of ridge; mined 

at southwest end where 

 it is only 5-25 ft. 

thick. 

(1) In zone 6 ft. thick 

near hanging wall; (2) 

in cleavelandite and 

quartz near quartz mass 

12 ft, thick at center 

of pegmatite.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 399

Table 8. New Hampshire mica and feldspar mines Continued

No.

87

88

89

90

91& J92q-i 

vo

Q4. 7^C

95

96

97

98

99

100

101

102

103

104

105

Name

Beryl Mountain.

John Balla. . 0

Cobb Hill....

Alien........

Klmball......

Harry Craig. .

Alstead (Lyman, Granite State,

Parsons ) .

Lakin prospect.

Damaziac. . . . .

Chickering. . .

Porter Bros. .

Gate So ..... .0

Product

P

P

FM

P

P

P

P

P

M

M

M

P

P

F

P

F

F

F

Character 

of mica

Small; mostly scrap.

l^Af^CTA V* wLJ.^0 . O QfOi > T*n'n CL^/

Light rum;

mostly

scrap.

Light green

or white;

mostly

scrap.

Little seen.

Little seen.

Little seen.

Light rum;

mostly A.

Light green,

stained;

A.

Light ruby,

bent.

Light rum,

some

specked;

also light

green,,

Light rum...

Light rum. . .

Light rum. . .

Green and

greenishrum wedge.

Mostly scrap

Yellow-green

wedge.

Little seen.

Little seen.

Notes on occurrence 

of mica

Feldspar prospect.

Two feldspar cuts,, At

north cut, small wedge

mica at contacts of

quartz with microcline.

Wedge mica at contacts of

quartz masses with

feldspar.

Three feldspar cuts. At

one, mica occurs on

lower side of inclusion

in large pegmatite.

Two open cuts for feldspar.

Large feldspar producer.

Feldspar mine; little

sheet mica seen.

Wedge mica with microcline and tourmaline in

quartz mass in pegmatite at least 50 ft.

thick.

Poorly exposed.

(1) Near quartz bodies,

or with quartz and

cleavelandite, in pegmatite at least 100 ft.

thick; (2) mostly near

hanging wall of pegmatite 10 ft. thick that

is probably an offshoot

from the larger pegmatite.

Small prospect in pegmatite at least 20 ft.

thick.

Feldspar mine; a little

mica near walls.

Three cuts. Most mica

seen .was beneath wall

rock pendant in southwest cut.

Two feldspar cuts. Mica

in center of one pegmatite 20-25 ft. thick,

associated with quartz

and microcline.

Small books with quartz

and plagioclase in

large pegmatite.

Mostly in quartz in pegmatite whose outcrop is

100 ft. wide.

Small mica occurs near

hanging wall.
400 STRATEGIC MINERALS INVESTIGATIONS, 1941

lOOFeet

\\ '',

A. -^ FtA «?r r»f "HOOA ~

EXPLANATION

Pegmatite Quartz-rnica schist

60ju- _._._- 

Strike and dip of foliation Contact of pegmatite with wall rock 

M

Mica workings Open cut

'>>,^* --___- 

Dump Feldspar stope

Figure UU. Sketch map of the Big mine.
MICA-BEARING PEGMATITES OP NEW HAMPSHIRE 401

Table 8. New Hampshire mica and feldspar mines Continued

No.

106

107

108 

1OQ

110

111

112

113

114

115 

lift

117

lift

119

Name

Surry prospect. 

Britton.

Smith Hill...

l*n*iOAn AT>,

Big (Davis, 

Rhoda ) .

Tripp No. I..

southwest 

of French.

Nichols 

(Keene Mica 

Products 

Co.)

Product

F

F

F 

F

FM

FM 

M

M

FM

M 

F

F

F

F

Character 

of mica

Cp o -rip a

Light greenish rum; 

wedge .

Light greenish rum. 

Not abundant

Light rumj 

minor A.

Light rum, 

nearly ruby; herringbone. 

Light ruby. .

(1) Cloudy

specked 

rum; (2) 

light 

green; (3) 

ruby.

Light rum; 

some 

stained.

Light rum. . .

Light greenish rum. 

Light rum...

and yellow 

green; 

some 

stained.

Notes on occurrence 

of mica

In large pegmatite at

northern of two prospects; intergrown with 

biotite. 

(1) With microcline in

central quartzose part 

of pegmatite 40 ft. 

thick; (2) near footwall. 

Feldspar mine, mica mostly scrap. 

Two feldspar prospects.

Pegmatite as much as 100 

ft. thick. Mica with 

quartz and plagioclase 

3-15 ft. from walls,- 

and in thinner parts of 

pegmatite to northeast 

and southwest, mostly 

near contacts. Also 

minor green A mica near 

quartz bodies, in central parts of large 

pegmatite. (See fig. 

44,) 

Mostly at contacts of 

quartz with plagioclase 

or microcline in large, 

irregular pegmatite. 

Along north edge of irregular outcrop of pegmatite 100 ft. across. 

Pegmatite contains 

large proportion of 

plagioclase feldspar. 

Distributed irregularly

through pegmatite 100- 

150 ft. thick, but more 

abundant near walls and 

inclusions. (See fig. 

45.)

Mrt Q "I" T TT V1AOT* mi O T*"t* *7 Vlf^HlACI

as much as 7 ft. thick 

in pegmatite more than 

30 ft. thick. 

Near walls and inclusions. 

Most abundant near 

hanging wall and largest 2-3 ft. from contacts. 

Partly intergrown with

biotite, in pegmatite 

more than 80 ft. thick. 

Not abundant. Feldspar

mine. 

Not abundant. Much

graphic granite.

Mrf^ Q 4" 1 tT YlftOT* TAI Q "1 T Q f^'f*

large pegmatite mined 

for feldspar.
402 STRATEGIC MINERALS INVESTIGATIONS, 1941

Contour interval IO feet 

Elevations based on arbitrary datum

Figure U5. Plan of the French mine.

Table 8. New Hampshire mica and feldspar mines Continued

No.

120

121

122

Name

Car on (Gory).

No name ( In

Gilsum) .

Isham (Low

White).

Product

P

M

M

Character 

of mica

Light rum. . .

Light rum;

herringbone.

Light runio..

Notes on occurrence 

of mica

Pegmatite 20-40 ft. thick

mined for feldspar.

Much intergrown with biotite.

Scattered through pegmatite 20 ft. thick, but

most abundant near

quartz 2 ft. thick in

middle 
MICA-BEARING PEGMATITES OF NEW HAMPSHIRE 403

Table 8. New Hampshire mica and feldspar mines Continued

No.

123

124 

125

126

127

1.2R

129

130

1 ^1

Name

High White...

Jehlal White.

Bingham Hill 

(Kirk No. 

1). 

Nims .........

PrM r>o

Aliber. ......

Product

M

M 

MF 

M

M

MF

M

F

MF

Character 

of mica.

Nearly 

white ; 

wedge, 

scrap. 

Light rum. . .

Light rum. . . 

Yellow green

some 

stainedo

Yellow

green; 

scrap. 

Yellow

green; 

stained.

Notes on occurrence 

of mica

In quartzose pegmatite at 

least 10 ft. thick.

Near ragged contacts of 

pegmatite 8-10 ft. 

thick. 

4-10 ft. below hanging 

wall in pegmatite 7-60 

ft. thick. 

Pegmatite 20 ft. thick.

Pegmatite at least 8 ft.

thick. 

Mostly near footwall of

pegmatite at least 40 

ft. thick. 

Mostly near hanging wall.

ably associated with 

cleavelandite . 

Mostly near walls of pegmatite 3-20 ft. thick, 

rich in cleavelandite.

o
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