UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

I \ , GEOLOGICAL SURVEY 

i, W. E. Wrather, Director

Bulletin 936

STRATEGIC MINERALS INVESTIGATIONS

1942

PART l, A-l

Short papers and preliminary reports by

T. L. KESLER, W. H. MONROE, DAVID GALLAGHER 

and others

.. .

:.- ' .v : : ..*::: . s 

. "» * * .

::.- .-. : ?.-. . , 

 . . :... .- «

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1944
Clv

 > . » . ;. . *
CONTENTS

[The letters in parentheses preceding the titles are those used to designate the papers for separate publication]

Page

(A) Muscovite in the Spruce Pine district, N. C., by 

T. L. Kesler and J. C. Olson (published in 

August 1942)..................................... 1

(B) 'Tungsten deposits of the Nightingale district, Pershing County, Nev., by W. C. Smith and P. W. 

Guild (published In August 1942)................. 39

(C) Topaz deposits near the Brewer mine, Chesterfield 

County, S. C., by Carl Pries, Jr. (published in 

August 1942).............*....................... 59

(D) Chromite and quicksilver deposits of the Del Puerto 

area, Stanislaus County, Calif., by H. E. Hawkes, 

Jr., F. G. Wells, and D. P. Wheeler, Jr. (published in August 1942)........................... 79

(E) Manganese deposits of Cedar Creek Valley, Frederick 

and Shenandoah Counties, Va., by W. H. Monroe 9 

(published in August 1942)....................... Ill

(F) Quicksilver deposits of the Parkfield district, 

Calif., by E. H. Bailey (published in November 

1942)................. .......................... 143

(G) Chromite deposits of Red Bluff Bay and vicinity,

Baranof Island, Alaska, by P. W. Guild and J. R. 

Balsley, Jr. (published in October 1942)......... 171

(H) Quicksilver deposits near the Little Missouri 

River, Pike County, Ark., by David Gallagher 

(published in October 1942)...................... 189

(I) Nickel-copper deposits on the west coast of

Chichagof Island, Alaska, by W. T. Pecora (published in September 1942)........................ 221

ILLUSTRATIONS

Page 

Plate 1. Map of the Spruce Pine district, N. C.,

showing locations of mines........... In pocket

 / 2. Geologic map and sections of the Nightingale tungsten district, Pershing County, 

Nev.................................. In pocket

^ 3. Geologic map of the Nightingale mine

area................................. In pocket

4. Geologic map of the Nightingale mine

workings.................................. 50

«/ 5. Geologic sections of the Nightingale mine

area................................. In pocket

6. Geologic map of Brewer mine and vicinity,

South Carolina............................ 62

*J 7. Map of topaz deposits near Brewer mine,

S. C................................. In pocket

III
IV ILLUSTRATIONS

Page

Plate 8. A, Irregular body of topaz rock In wall of 

open pit; B_, Banded topaz rock cut by 

veinlets of "bull" quartz; (3, Brecciated 

silicified rock partly replaced by topaz.. 66 

9. Map of new excavation for topaz rock near

the Brewer mine, August 1941.............. 70

^ 10. Geologic map of the ultrabasic complex of 

Del Puerto area, Stanislaus County, 

Calif................................ In pocket

11. Geologic map of Adobe Canyon chromite area.. 98

12. Map of part of northern Virginia showing

location of Cedar Creek Valley............ 114

J 13. Geologic map and sections of part of Cedar 

Creek Valley, Va., showing location of 

manganese mines and prospects........ In pocket

14. Geologic map of the Mineral Ridge mine...... 122

15. Geologic map of the Bonnet Hill and Godlove

mines..................................... 130

«* 16. Geologic map and sections of Capola mountain, Va............................. In pocket

17. -Geologic map and sections of the Patrlquin 

. area, Calif............................... 146

 ^ 18. Map and sections of the Patrlquin mine. In pocket 

19. Geologic map and section of the Table Mountain area, Calif.......................... 146

£0. Map and section of the White mine........... 166

21. Geologic reconnaissance map of central

Baranof Island, southeastern Alaska....... 174

22. Geologic map of the Red Bluff Bay area,

Baranof Island, southeastern Alaska....... 178

 23. Geologic and topographic map of part of the

southwestern Arkansas quicksilver district,

showing location of areas mapped in

detail............................... In pocket

24. Surface map of Lowrey and James prospect.... 204

25. Surface map of Craig mine................... 204

26. Underground map of Craig mine............... 204

27. Surface map of Hopkins Hill................. 204

28. Surface map of U. S. Mercury Co. and Hales

Mining & Development Co. property......... 208

29-. Underground map and sections of U. S.-Merv cury Co. mine............................. 208

4 30. Surface map of Parnell Hill............ In pocket

31. Surface map of Parker Hill.................. 212

32. Surface map of East Gap Ridge............... 212

33. Surface map of Gap Ridge.................... 216

34. Surface and underground map of South Mill

Mountain.................................. 216

35. Surface and underground map of Big Six mine. 216

36. Geologic map of the stock hear Davison Bay,

Chichagof Island, Alaska.................. 228

37. Map showing prospect pits and tentative surface ^outline of the disseminated-sulfide 

deposit, Chichagof Island................. 236

Figure 1. Index map showing location of the Spruce

Pine district, North Carolina............. 3

2. Index map of Nevada showing location of

Nightingale tungsten district............. 40

3. Map of South Carolina showing location of

topaz deposits near Brewer mine........... 60

 4. Index map showing location of Del Puerto

area, Stanislaus County, Calif............ 80

5. Geologic sketch map of Del Puerto area...... 84

6. Typical chromite structures................. 93

7. Geologic map of Black Bart chromite area.... 99

8. Plan of Black Bart chrome mine.............. 100
ILLUSTRATIONS V

Page 

Figure 9. Plan and section of Black Bear chrome mine.. 101

10. Plan of Lucky Girl chrome mine.............. 102

11. Map of Adobe Valley quicksilver area........ 106

12. Plan of Adobe Valley quicksilver mine....... 107

13. Plan of WInegar quicksilver prospect........ 109

14. Map showing location of the Parkfield district, Calif., and the areas comprising 

plates 17 and 19.......................... 145

15. Index map of southeastern Alaska showing

location of the Red Bluff Bay area........ 172

16. Geologic sketch map of deposit No. 2........ 183

17. Index map showing location and extent of the/

southwestern Arkansas quicksilver district/ 190

18. Indealized sketch of Z-bends and a series of

S-bends............................... 0 ../. 195

19. Underground map and section of Hales mine../. 208

20. Underground map of Parnell Hill adit...... J. 210

21. Level maps and section of Parker Hill mine/. 213

22. Index map of southeastern Alaska showing / 

location of the nickel-copper deposits on 

the west coast of Chichagof Island....,'... 223

23. Generalized geologic map of a part of

western v Chichagof Island.................. 227

24. Sketch map showing outcrop of concentratedsulfide deposit near the shaft on Fleming 

Island.................................... 231

25. Geologic map of .the south shore of a protected cove near the head of Davison Bay.. 234

26. Sketch map of outcrop of concentrated- \ 

sulfide deposit in norite near the head of 

Davison Bay............................... 235

TABLES

Page

Table 1. Average composition of alaskite from the 

Davis quarry and of pegmatite from the 

Deer Park No. 5 mine (155)................ 6

2. Summary of the occurrence of mica in the

Spruce Pine district...................... 12

3. Power factors of muscovite from the Spruce

Pine district, N. C....................... 20

4. Distribution of power-factor values of

Spruce Pine muscovite, summarized from

table 3................................... 24

5. Comparative results of power-factor measurements made in August and December 1940.... 24

6. Table showing relation by weight of finished

condenser films to raw mica................ 26

7. Results of electrical tests by R. C. A...... 29

8. Table showing intermittent operation of mica

mines in the Spruce Pine district......... 31

9. Price range of clear sheet mica in the

Spruce Pine district, 1917-40............. 32

10. Recorded production of sheet and punch mica 

from North Carolina, compared with total 

for the United States, including North 

Carolina.................................. 33

11. Analyses of recorded production of sheet and 

punch mica from the Spruce Pine district, 

N. C................................. In pocket
VI TABLES

Page

Table 12. Analysis of aggregate production of sheet 

mica from 130 mines in the Spruce Pine 

district, 1917-40......................... 36

13. Chemical analyses of topaz rock............. 69

14. Grade of topaz placer....................... 75

15. Reserves of topaz in placer ground.......... 77

16. Weather records for Kimshan Cove, Alaska,

from August 1940 to September 1941........ 225

17. Analytical data and ratios of nickel to copper and of sulfur to nickel plus copper, 

in samples from the nickel-copper deposits 

on the west coast of Chichagof Island..... 238

^m-^ 

 -«'.
A Page

Abstracts of reports.... 1, 39, 59-60, 79,

111, 143-144, 171, 189, 221-222 

Acknowledgments for aid.... 4, 42, 62, 81,

112-113, 146, 173, 191, 222 

Adobe Canyon mine, features of..... 96-97,

p'l. 11 

Adobe Valley mine, features of.... 105-108

Alaska, chromlte deposits In..... 171-187,

pis. 21-22 

nickel-copper deposits In..... 221-243,

pis. 36-37 

Alasklte, composition of............. 6

Allied Manganese Corporation, operations by....................... 136

American Alloy Corporation, operations by. .................. 124, 128

Arkansas, quicksilver deposits In.... 189-

219, pis. 23-35 

Arkansas Power & Light Co., property

of............................. 214

Arkansas Quicksilver Corporation,

operations by.............. 212, 215

B

Bailey, E. H., Quicksilver deposits

of the Parkfleld district,

Calif........... 143-169, pis. 17-20

Balsley, J. R., Jr., Guild, P. W.,

and, Chromlte deposits of Red

Bluff Bay and vicinity, Baranof

Island, Alaska.. 171-187, pis. 21-22 

Baranof Island, Alaska, chromlte

deposits on..... 171-187, pis. 21-22

Big Six mine, features of........ 218-219,

pi. 35 

Big Six Mining Co., operations by.... 218

Big Six Mining Co., The, operations

by............................. 218

Black Bart claims, features of..... 98-101

Black Bear mine, features of...... 101-102

Bonnet Hill mine, features of.... 130-132,

pi. 15 

Brewer mine, S. C., geology of area

near..j................ 62-64, pi. 6

topaz deposits near.... 59-78, pis. 6-9

Brill prospect, features of....... 128-129

Bureau of Mines, drilling and trenchIng by....... 42, 52-53, 191, pis. 3, 5

California, quicksilver deposits In.. 143-

169, pis. 17-20

Capola Mountain mine, geology of..... 138-

139, pi. 16 

history and production of...... 135-136

ore body In.................... 139-141

workings of............ 136-137, pi. 16

Cedar Creek Valley, Va., field work

In............................. 112

geography of................... 113-114

geology of............. 114-117, pi. 13

history of manganese mining In.... 117-

118 

manganese deposits In......... 111-141,

pis. 12-16 

manganese production from......... 118

Chesterfield County, 3. C., field

work In....................... 61-62

topaz deposits In...... 59-78, pis. 6-9

Chlchagof Island, Alaska, geography

of.......................... 222-225

geology of............. 226-229, pi. 36

nickel-copper deposits on.... 221-243,

pla. 36-37

Page

Chrome Camp mine, features of..... 103-104

Chromlte deposits, Red Bluff Bay,

Baranof Island, Alaska..... 171-187,

pis. 21-22 

Del Puerto area, Calif......... 79-110,

pla. 10-11 

Chromlte production, Del Puerto area,

Calif.......................... 82

Chromlte samples, analyses of..... 91, 181

Copper deposits, Chlchagof Island,

Alaska.......... 221-243, pis. 36-37

Copper-nickel samples, analyses of... 237-

239 

Craig mine, features of.......... 203-204,

pis. 25-26 

Cralg Mining Co., operations by...... 203

Crockett Mining Co., operations by... 207

Dawson mine, features of............. 166

Del Puerto area, Calif., chromlte and

quicksilver deposits of..... 79-110,

pis. 10-11 

ehronite production from.......... 82

field work In..................... 81

geology of........... 83-90, pis. 10-11

history of mining in............. 81-83

quicksilver production from....... 83

Don claim, workings on............... 56

E

East Gap Ridge workings, features

of.................. 214-215, pi. 32

Frederick and Shenandoah Counties,

Va., manganese deposits In..... HI141, pis. 12-16

Fries, Carl, Jr., Topaz deposits near 

the Brewer mine. Chesterfield 

County, S. C........ 59-78, pis. 6-9

G. W. D. mine, features of........ 162-163

Gallagher, David, Quicksilver deposits near the Little Missouri 

River, Pike County, Ark.... 189-219,

pis. 23-35 

Gap Ridge mine, features of...... 215-217,

pi. 33 

Garfleld Force property, features

of............................ 53-54

tungsten production from.......... 48

Geologic maps:

Arkansas quicksilver district... pi. 23 

Brewer mine and vicinity, 3. C... pi. 6 

Cedar Creek Valley, Va.......... pi. 13

Central Baranof Island, Alaska., pi. 21 

Del Puerto area, Stanislaus

County, Calif................ pi. 10

Nightingale district, Pershlng

County, Nev................... pi. 2

Patrlquln area, Calif........... pi. 17

Red Bluff Bay area, Alaska...... pi. 22

Stock near Davison Bay, Chlchagof

Island, Alaska............... pi. 33

Table Mountain area, Calif.... pi. IX

Gillette prospect, features of....... 16i>

Godlove mine, features of........ 1.29-.'».' '>

yji, 

Gold-Silver-Tungsten Co., Inc.,

property of..... 41-42, 48-49, 54-b&
VIII

Page

Guild, P. W., and Balsley, J. R., Jr., 

Chromite deposits of Red Bluff 

Bay and vicinity, Baranof 

Island, Alaska.. 171-187, pis. 21-22

Guild, P. W., Smith, W. C., and,

Tungsten deposits of the Nightingale district, Pershing 

County, Nev......... 39-58, pis. 2.-5

H

Hales mine, features of... 207-209, pi. 28

Hales Mining & Development Co.,

property of............. 207, pi. 28

Hall, E. L., power factor tests by... 4,

18-25

Hawkes, H. E., Jr., Wells, F. G.,

Wheeler, D. P., Jr., Chromite 

and quicksilver deposits of the 

Del Puerto area, Stanislaus 

County, Calif.... 79-110, pis. 10-11

Hopklns Hill workings/ features of... 204-

205, pi. 27

Hy-Grade Manganese Co., operations

by..................... 123-125, 128

Hy-Grade Production & Sales Corporation, operations by.... 124-125,«128

K

Kesler, T. L., and Olson, J. C.,

Muscovite in the Spruce Pine 

district, N. C.......... 1-38, pi. 1

Kings mine, features of........... 164-165

Limestone Ridge prospects, features

of.......................... 122-123

Little Missouri River, Ark., quicksilver deposits near....... 189-219,

pis. 23-35

Lowrey and James prospect, features

of.................. 202-203, pi. 24

Lucky Girl mine, features of...... 102-103

H

McCune prospect, features of......... 128

Mammoth claim, tungsten deposits on. 54-56 

Manganese, deposits, Cedar Creek

Valley, Frederick and Shenandoah Counties, Va.......... 111-141,

pis. 12-16 

Manganese ore, analyses of........... 127

Mercury Producers, Inc., operations

.by............................. 209

Mica, electrical tests on........... 28-30

grading and prices of............ 31-33

mode of occurrence of...... 9-11, 12-13

physical properties of........... 11-18

power factor measurements of..... 18-25

Spruce Pine district, H. C. 1-38, pi. 1 

uses of........................... 1-2

Mica mining, in the Spruce Pine district, N. C., history of...... 30-31

Mica production, in Spruce Pine district, H. C................... 33-36

Mineral Ridge mine, geology of... 125-126,

pi. 14 

history and production of...... 123-124

ore body in.................... 126-127

workings of............ 124-125, pi. 14

Monroe, W. H., Manganese deposits of 

Cedar Creek Valley, Frederick 

and Shenandoah Counties, Va.... 111-

141, pis. 12-16 

Muscovite, Spruce Pine district,

H. C.................... 1-38, pi. 1

N

National Bureau of Standards, power

factor tests by............... 18-25

Nelson No. 1 prospect, features of... 122

Page

Nelson No. 2 prospect, features of... 122 

Nevada, tungsten deposits in....... 39-58,

pis. 2-5

Nickel-copper samples, analyses of... 237-

239 

Nickel deposits, Chichagof Island,

Alaska.......... 221-243, pis. 36-37

Nightingale district, Nov., geology

of.................. 42-48, pis. 2-3

tungsten deposits in... 39-58, pis. 2-5 

Nightingale nine, tungsten deposits

of.................'.'. 48-53, pis. 3-5

tungsten production from.......... 48

workings of.............. 48-49, pi. 4

North Carolina, mica deposits in.... 1-38,

pi. 1

North end prospects, tungsten deposits on........................ 54-56

No. 5 group of Chromite claims,

features of........... 97-98, pi. 11

Ore deposits. Cedar Creek Valley,

Va.......................... 117-121

Chichagof Island, Alaska...... 229-239,

pi. 37

Del Puerto area, Calif.. 91-95, 104-105 

Nightingale district, Hev........ 48-56

Parkfleld district, Calif...... 156-160

Pike County, Ark............... 196-201

Red Bluff Bay, Alaska.......... 178-185

Ore reserves, Cedar Creek Valley,

Va.......................... 120-121

Chichagof Island, Alaska....... 240-241

Del Puerto area, Calif...... 95-96, 105

Nightingale district, Nev........ 57-58

Parkfleld district, Calif...... 167-168

Pike County, Ark............... 200-201

Red Bluff Bay, Alaska.......... 185-187

Olson, J. C., Kesler, T. L., and, 

Muscovite in the Spruce Pine 

district, N. C.......... 1-38, pi. 1

Orndorff, James, prospect, features

of.......................... 133-134

Orndorff, Mary, prospect, features

of.......................... 132-133

Orndorff, Moses, prospect, features

of............................. 123

Orndorff, R. L., prospect, features

of............................. 134

Orndorff, Ralph, prospect, features

of............................. 135

Orndorff, Rhesa A., prospect, fea-'

tures of....................... 132

Ozan-Graysonla Lumber Co., property

of............... 202, 203, 205, 207

Parker Hill mine, features of.... 212-214,

pi. 31 

Parkfield district, Calif., field

work In..................... 145-146

geology of........ 146-155, pis. 17, 19

quicksilver deposits In....... 143-169,

pis. 17-20

quicksilver production from... 146, 147 

Parnell Hill workings, features of... 209-

212, pi. 30 

Patriquln mine, f eatxires Of...... 160-168,

pi. 18

Pecora, W. T., Nickel-copper deposits 

on the west coast of Chichagof 

Island, Alaska.. 221-243, pis. 36-37 

Peer, Cleve, prospect, features of... 134 

Peer, Frank, prospect, features of... 133 

Perahlng County, Nev., tungsten

deposits of......... 39-58, pis. 2-5

Pike County, Ark., field work in..... 191

quicksilver belt, geology of.. 191-196,

pi. 23 

quicksilver deposits in....... 189-219,

pis. 23-35 

Poppy mine, features of.............. 163
INDEX XX

Prospectlng, suggestions for. In the 

Del Puerto area, Calif.........

In the Parkfield district, Calif..

Page Page

Stanislaus County, Calif., ohromlte 

95 and quicksilver deposits In. 79-110, 

168- pis. 10-11 

169 Summit mine, features of............. 110

Quicksilver deposits, Del Puerto

area, Calif...... 79-110, pis. 10-11

Parkfield district, Calif..... 143-169,

pla. 17-20

Pike County, Ark... 189-219, pis. 23-35 

Quicksilver production, Del Puerto

area, Calif................. 82, 105

Parkfield district, Calif..... 146, 147

Pike County, Ark.............. 199, 201

R. C. A. Manufacturing Co., electrical toata by.................. 28-30

fabrication tests by............. 27-28

Rattlesnake prospect, features of.... 167

Red Bluff Bay area, Alaska, chroaiite

deposits in..... 171-107, pis. 21-22

field work in..................... 173

geology of............. 174-178, pi. 22

Schoolite .Extension claim, tungsten

deposits on.................... 56

Scintilla Magneto Division, Bendix 

Aviation Corporation, fabrication tests by.................. 26

Shenandonh and Frederick Counties,

Va., manganese deposits In. 111-141, 

pis. 12-16

Smith, W. C., and Guild, P. W., Tungsten deposits of the Nightingale district, Pershlng County, 

Nev................. 39-58, pis. 2-5

Sommer's prospect, features of..;. 163-164

South Carolina, topaz deposits in.. 59-78,

pis. 6-9

South Mill Mountain prospects, features of................ 217, pi. 34

Southern Kraft Paper Co., property 

of............................

Southern Ores, Inc., operations by.. 

.Southwestern Quicksilver Co., operations by......................

Spruce Pine district, N. C., field 

work in.......................

geology of

214

135

209

3-4 

4-11 

muscovlte in............... 1-38, pi. 1

570234 O - 44 - 2

Topaz, analyses of.................. 68-69

Topaz deposits, Chesterfield County,

S. C................ 59-78, pis. 6-9

. geology of................ 64-70, 73-74

grade of........... 70-72, 74-76, pi. 7

Topaz reserves, Chesterfield County,

S. C................... 72-73, 76-77

Tungsten deposits. Nightingale district, Pershlng County, Nov.. 39-58, 

pla. 2-5

U

U. S. Mercury Co., property of....... 204,

205-207, pis. 28-29 

United Feldspar ft Minerals Corporation, analyses by.............. 6

operations by................... 61, 70

Van Buren Furnace Co., operations by. 135 

Virginia, manganese deposits in.. 111-141,

'pis. 12-16

W

Wells, F. 0., Wheeler, D. P., Jr.,

Hawkes, H. E., Jr., and, Chromite and quicksilver deposits 

of the Del Puerto area, 

Stanislaus County, Calif.... 79-110, 

pis. 10-11

West Coast Chrome Co., property of. 82-83,

96

Wheeler, D. P., Jr., Wells, F. 0.,

Hawkes, H. E., Jr., and, Chromlte and quicksilver deposits 

of the Del Puerto area, 

Stanislaus County, Calif.... 79-110, 

pis. 10-11

White mine, features of... 166-167, pi. 20

Wlnegar prospect, features of..... 108-110

Yenglln prospect, features of. 204

o
UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 936-A

MUSCOVITE IN THE SPRUCE PINE DISTRICT 

NORTH CAROLINA

 BY

T. L. KESLER AND J. C. OLSON

Strategic Minerals Investigations, 1942 

(Pages 1-38)

UNITED STATES

GOVERNMENT'PRINTING OFFICE 

WASHINGTON : 1942

For sale by the Superintendent of Documents, Washington, D. C. ------- Price 35 cents

CONTENTS

Page

Abstract..............» ............................... ... 1

Introduction............................................. 1

Geologic setting......................................... 4

Schists and gneisses. ............................... . 4

Alasklte............................................. 5

Pegmatite............................................ 5

Origin........................................... 6

Relations to wall rocks.......................... 7

Basalt............................................... 9

Occurrence of muscovlte.............................. 9

Properties affecting the value of muscovlte.............. 11

Cleavage........................................... * . 11

Flexibility and elasticity........................... 15

Color................................................ 15

Staining and inclusions.............................. 16

Natural distortion................................... 17

Power factor......................................... 18

Tests of Spruce Pine muscovite........................... 18

Measurements of power factor......................... 18

Tests to determine utility in condensers............o 25

Tests made by the Scintilla Magneto Division,

Bendix Aviation Corporation, Sidney, N. Y...... 26

Fabrication of mica.......................... 26

Comments by Scintilla........................ 26

Tests made by the R. C. A. Manufacturing Co.,

Inc., Camden, N. J............................. 27

Descriptions and fabrication of mica......... 27

Results of electrical tests.................. 28

Comments by R. C. A.......................... 28

Mining and marketing..............................»...... 30

History of mining.................................... 30

Grading and prices................................... 31

Production........................................... 33

Future possibilities..................................... 36

ILLUSTRATIONS

Page 

Plate 1. Map of the Spruce Pine district, North

Carolina, showing locations of mines.... In pocket 

Figure 1. Index map showing location of the Spruce

Pine district, North Carolina........... 3

III
TABLES

Page

Table 1. Average composition of alaskite from the Davis 

quarry and of pegmatite from the Deer Park 

No. 5 mine (155) ............................... 6

2. Summary of the occurrence of mica in the

Spruce Pine district!........................ 12

3. Power factors of muscovite from the Spruce

Pine district, North Carolina................ 20

4. Distribution of power-factor values of Spruce

Pine muscovite, summarized from table 3...... 24

5. Comparative results of power-factor measurements made in August and December 1940......» 24

6. Table showing relation by weight of finished

condenser films to raw mica.................. 26

7. Results of electrical tests by R. C. A......... 29

8. Table showing intermittent operation of mica

mines in the Spruce Pine district............ 31

9. Price range of clear sheet mica in the Spruce

Pine district, 1917-40....................... 32

10. Recorded production of sheet and punch mica

from North Carolina, compared with total for

the United States, including North Carolina.. 33

11. Analyses of recorded production of sheet and 

punch mica from the Spruce Pine district, 

North Carolina.......................... In pocket

12. Analysis of aggregate production of sheet 

mica from 130 mines in the Spruce Pine 

district, 1917-40............................ 36

IV
MUSCOVITE IN THE SPRUCE PINE DISTRICT, NORTH CAROLINA

By T. L. Kesler and J. C. Olson

ABSTRACT

The recorded production of sheet and punch mica from North 

Carolina-since 1868 Is 25,563,341 pounds, of which the Spruce 

Pine district has produced 16,600,000 pounds or more. The district's production of relatively clear sheet mica, larger than 

punch, has averaged about 45,000 pounds a year since 1924. Some 

of this, although the proportion cannot be determined, is apparently as good as the higher grades of imported mica used in the 

manufacture of radio equipment, airplane spark plugs, transformers, and generators. Sheet mica of highest quality is indispensable for these purposes, and is classed as a strategic 

mineral.

The Spruce Pine mica Is mined from pegmatite bodies that 

range from a few inches to more than a hundred feet in thickness. 

Their source is a coarse-grained granite, termed alaskite, which 

crops out principally north and west of Spruce Pine. About 225 

mines have been operated for mica, with feldspar a prominent 

byproduct. About 289 mines have been operated for feldspar, 

with mica commonly a byproduct.

This report describes the occurrence of the mica and its 

physical properties among which is an unusually wide range of 

colors. A table is presented showing the results of powerfactor measurements made by the National Bureau of Standards on 

196 samples of sheet mica from 109 mica mines and 15 feldspar 

mines. Samples from 71 of the mines have power factors within 

the limits allowed for use in radio-transmitter condensers. 

Other tables show the results of fabrication and electrical 

tests of samples from 10 mica mines in North Carolina, 6 of 

them in the Spruce Pine district, as determined by two commercial users of mica, who concluded that the mica in 8 of the 10 

samples is suitable for use in condensers.

It is concluded that more systematic planning of mica mining, 

for the district as a whole, would result in an average yearly 

production of at least 90,000 pounds of relatively clear sheet 

and possibly much more. Tables analyzing the recorded production of many mines, both individually and in the aggregate, are 

included for use in anticipating future production.

INTRODUCTION

Sheet mica of the highest quality is used as the dielectric 

in condensers for radio and long-distance telephone, for the

1
2 STRATEGIC MINERALS INVESTIGATIONS, 1942

manufacture of airplane motor spark plugs, as- bridges and spacers in radio tubes, as insulation in transformers, for commutator segments and V-rings, and for armature insulation in motors 

and generators. Only a small part of the world's total production of mica is flat, clear, and flawless enough, and of such 

low power factor, as to be usable for these purposes; and the 

United States has depended very largely on foreign sources for 

its supply.

The Spruce Pine district was selected for Investigation because it is the principal mica-producing area of the United 

States. What proportion of the clear sheet mica produced from 

the district has been of the quality now of strategic value is 

not known, for the final test of such quality is industrial 

use, and, unfortunately, it is impossible to trace all the uses 

to which Spruce Pine sheet mica has been put, much less the 

amounts involved in each useThe district, which is in the Blue Ridge physiographic 

province, centers in the town of Spruce Pine (population 1,968), 

and includes parts of Yancey, Mitchell, and Avery Counties, in 

western North Carolina (see fig. l)o The three counties have a 

combined population of 46,743, a large proportion of which has 

taken some part in the mining and manufacturing of mica. The 

industrial mineral plants in the district comprise three feldspar grinding mills, two clay refineries, seven plants for 

grinding muscovite, one plant for grinding blotite, and three 

factories that cut and fabricate muscovite. The Carolina, 

Clinchfleld, and Ohio Railroad passes through Spruce Pine, and 

the district is also served by 65 miles of paved highways, 125 

miles of relatively good graded roads, and numerous temporary 

mining and logging roadso

\] Welrum, H. P., and others, The mica industry: U. S. Tariff Commission Kept. 130, 2d ser., pp. lU-23, 1938.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 3

The area of the district is 250 square miles, and its longest dimension, from northeast to southwest, is 25 miles. Altitudes range from 2,150 feet on the Toe River, west of Bakersville, to 6,684 feet on Mount Mitchell, southeast of Burnsville. 

Most of the region is drained by the North Toe and South Toe 

Rivers, which unite near Micaville to form the Toe, a northwestflowing tributary of the Nolichucky River.

EST VIRGINIA *|

. S iV I R G I fl

*Lynchburg 

 Roanoke

Figure 1.- Index map showing location of the Spruce Pine district. 

North Carolina.

2/ The geology of the region has been described by Keith, and

some of the pegmatite bodies that have been mined have been des3/ 4/ cribed by Sterrett and Maurice."

The authors' field work in the district began in November 

1939 and continued until the end of May 1940; later developments 

were examined in July 1940 and May 1941. The field work was 

carried on largely by Olson, assisted by F. W. Hinrlchs, but

?/ Keith, Arthur, U. S. Geol. Survey Geol. Atlas, Cranberry foliq (No. 

90), 1903; Mount Mitchell folio (No. 12U), 1905; Roan Mountain folio (No. 

151), 1907.

3/ Sterrett, D. B., Mica deposits of the United States: U. S. Geol. Survey Bull. 7to, PP. 177-1SU, 2^5-261, ?73-?79, 19?3.

U/ Maurice, C. S., The pegmatites of the Spnice Pine district. North Carolina: Econ. Geology, vol. 35, pp. U9-78, 15EMLg7,
4 STRATEGIC MINERAL INVESTIGATIONS, 1942

Kesler was in the-field for 2 months. Examinations of 219 mica 

mines and 110 feldspar mines were made. The locations of these 

mines, and also of those not examined in detail, are shown on 

plate 1, a topographic map of the district.

Operators, miners, and buyers without exception cooperated 

heartily throughout the course of the work. Thanks are due to 

Mr. E. L. Hall, of the National Bureau of Standards, for determining power factors of 196 specimens of mica from 109 mines, 

and to the Bureau for permission to publish the results. The 

laboratories of the Scintilla Magneto Division of the Bendix 

Aviation Corporation and of the R. C. A. Manufacturing Corporation, Inc», fabricated and tested, in order to determine its 

suitability for commercial use in condensers, mica collected 

from six mines in the district and from four mines elsewhere in 

North Carolina. The writers are indebted to these companies for 

permission to publish the results of their tests, and particularly for the cooperation of Mr. Tullio Tognola, of the Scintilla Magneto Division, and of Mr. R. Howell, of the R. C. A. 

Manufacturing Corporation.

GEOLOGIC SETTING 

Schists and gneisses

Interlayered mica schists and gneisses and hornblende 

gneisses underlie most of the district; less abundant metamorphic rocks are kyanite-garnet gneiss, graphitic muscovite schist,

5/ marble, and soapstone. Keith considered these rocks to be of

pre-Cambrian age. In general they strike northeast and dip 

southeast, but other attitudes prevail over considerable areas.

Dips in the western and southwestern parts of the district mostly exceed 45 ; those elsewhere are gei 

the horizontal in the northeast part.

ly exceed 45 ; those elsewhere are generally less, approaching

Keith, Arthur, op. cit.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 5 

Alaskite

A medium- to coarse-grained granite, in part pegmatltic, 

crops out in the central part of the district. The rock consists of potash feldspar, sodic plagioclase, quartz, a very little muscovite, and mere traces of dark minerals. It has been 

termed alaskite by Hess and Hunter.-/ The composition of typical 

material, quarried a fourth of a mile east of Minpro, is shown 

in table 1. The alaskite probably is late Paleozoic in age.

The structural relations of alaskite to the schists and 

gneisses can be observed best in open-cut mines at localities 

where the alaskite has been weathered to clay. In these exposures, the alaskite appears to be intrusive into the metamorphic 

rocks, mostly as irregular, sill-like bodies that extend along 

the strike of the wall rocks but do not everywhere conform to 

them in detail<> The alaskite bodies contain slablike inclusions, 

mostly oriented parallel to the foliation of the wall rocks. 

The alaskite bodies range in length from a few hundred.feet to 

perhaps a mile or more. Their contacts are commonly sharp, but 

muscovite schists marginal to some alaakite bodies have been impregnated with feldspars and quartz.

Pegmatite

The pegmatite bodies of the Spruce Pine district range in 

size from podlike bodies less than an inch across, developed in 

wall rocks near larger bodies of pegmatite and alaskite, to 

bodies a hundred feet or more in thickness. Forty-four minerals 

have been found in them, but their principal constituents are 

oligoclase, microcllne, quartz, albite, and muscovite. The relative proportions of these minerals vary greatly in different 

parts of some individual bodies, and sharp contrasts in the bulk

6/ Hunter, C. E., Residual alaskite kaolin deposits of North Carolina: 

An. Ceramic Soc. Bull., vol. 19, p. 98,

454759 O - 42 - 2
6 STRATEGIC MINERALS INVESTIGATIONS, 1942

compositions of adjacent bodies are common. Differences in "composition, together with other mineralogic, economic, and textural features, have been used by Maurice /in an elaborate classification of Spruce Pine pegmatite and a theory of its origin.

8/ Holmes has computed the age of uranlnite from the Plat Rock

9/ 

mine (147) as 251 million years--late Carboniferous or early

Permian.

Origin.--Every well-exposed body of alaskite in the district 

contains irregularly shaped masses of pegmatite which range in 

maximum dimensions from a few inches to several hundred feet. 

These pegmatite masses characteristically have transitional contacts with the alaskite and consist of the same essential minerals, the only apparent differences between the two rock types 

being in grain size and muscovite content, which generally is 

higher in pegmatite Their similarity in chemical composition 

is shown in table 1.

Table 1»--Average composition of alaskite from the Davis quarry 

and of pegmatite from the Deer Park No, 5 mine (155) I/

Si02 . .00.0............

A1 203 .. ................

FeoOv ................ £< w

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

KgO ...................

Na 20. ..... o = .. o .......

Tn i~fl 1

Average from 500 

tons alaskite 

(percent)

74- Q

1 4 Q

 Z-2

1.0

4 7

4.0

.2

100 o 03

Weighted average from 

47,992 tons pegmatite 

(percent)

7S 9P,

14 92

,28

1 = 10

A i q

4 20

.28

100.23 f?:

iy Analyses by United Feldspar & Minerals Corporation* kinpro, N. C. 

Published by permission of Ur. B. C. Burgess,

These pegmatite masses are neither inclusions of rock older 

than alaskite nor intrusive bodies younger than alaskite. The

ZJ Maurice, C. S., op. cit.

ZJ Holmes, Arthur, Physics of the earth, part IV, the age of the earth: 

Nat. Heeearch Council Bull. SO, pp. 3^-344, 1931.

2/ lumbers in parentheses refer to the mine numbers used in plate 1 and 

the accompanying lists of mines.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 7

Intergradation of textures and similarity of compositions of the 

two establish their genetic relationship, the pegmatite apparently having been formed while the alaskite crystallized, 

through the medium of solutions expelled into openings that 

formed contemporaneously by shrinkage.

Emanations from the crystallizing alaskite were also driven 

into zones of weakness in the schists and gneisses, forming pegmatite bodies at various distances from the alaskite. Some of 

these bodies contain alaskitic rock that intergrades with the 

coarser pegmatitic rock. This condition is similar to that in 

alaskite bodies that contain pegmatite masses, except that the 

relative proportions of the two rock types are reversed. Pegmatite bodies in the metamorphic rocks have been the principal 

sources of mica, but many of them have yielded much feldspar.

Relations to wall rocks. The 62 commercially developed pegmatite masses in alaskite that were examined have random and unpredictable attitudes, and no consistent structural relations 

between pegmatite masses and enclosing alaskite could be established.

Pegmatite bodies in the schists and gneisses are mostly tabular, but some are lenticular in cross section. Of those examined, 195 are generally conformable in attitude with the 

layers of their wall rocks, 22 are crosscutting, and the attitudes of 50 could not be determined because of inadequate exposures. Conformable lenticular bodies commonly occur in closely 

spaced imbricate arrangement, and a group of such bodies may be 

mined as a unit. The operation is simplified where the lenticular bodies are connected by thin, tabular extensions of pegmatite, forming composite bodies known locally as "pinch-andswell" or "peanut veins".

Contacts with hornblendic wall rocks are relatively sharp, 

but the hornblende commonly is altered to biotite in a contact 

zone ranging from a few inches to several feet in thickness.
8 STRATEGIC MINERALS INVESTIGATIONS, 1942

Contacts with mica schists are frequently gradational owing to 

Impregnation of the wall rocks by pegmatitic feldspar and quartz, 

which is well shown at the Googrock (255) and Bailey Mountain 

(307) mines. Many pegmatite bodies contain inclusions of wall 

rocks, mostly tabular or slablike and generally oriented parallel to the walls. The contacts between inclusions and pegmatite 

are commonly indistinct as a result of partial replacement of 

the inclusions by pegmatitic feldspar and quartz.

Near Plumtree and Ingalls most of the pegmatite bodies in 

the schists and gneisses are nearly horizontal (see pi. 1), and 

few of them dip more steeply than 30°. From the vicinity of 

Spruce Pine southwestward to Celo, most of these bodies strike 

northeast and dip 30°-45° SE. Alaskite bodies in this area have 

similar attitudes, but, as already stated, pegmatitic masses in 

the alaskite bodies have random attitudes. Bodies in the northwestern part of the district, from the head of Henson Creek 

southwestward to Micaville and Burnsville, strike more or less 

uniformly northeastward and dip 60°-80° SE. Most of the bodies 

south, of Celo and in the northern part of the Black Mountains 

strike northwest to north and dip southwest. A few are definitely pipelike and pitch southwestward.

Groups of adjacent pegmatite bodies that are similar in composition and contain muscovite of the same color almost invariably lie parallel to the structural trend of the country rocks. 

This suggests that the -composition of wall rocks influenced the 

composition of pegmatite. A result, from the practical standpoint, is a general correlation between the quality of mica and 

the character of wall rocks; for example, pegmatite having kyanitlc wa],l rock yields mica of ruby color almost exclusively, 

and that in alaskite contains mostly green and greenish-rum 

mica.

There has been some relatively minor deformation of the 

pegmatite, reflected by faults of slight displacement, by frac-
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 9 

tured feldspar crystals, and by ruled and bent mica crystals.

Basalt

A few dikes of fine-grained basalt, mostly less than 5 feet 

in thickness, cut the other rocks in the district, including

pegmatite. Dikes of the basalt are exposed at the Peru (6),

107 

Puncheon Camp (11), and Elk (24) mines. Keith has correlated

these dikes with the Triassic diabase of the Piedmont. 

Occurrence of muscovlte

Muscovite is distributed sporadically in pegmatite throughout the district. Commercially valuable mica, however, is localized in shoots called "streaks" in which mica generally constitutes 2 to 6 percent of the rock, or even as much as 40 percent in exceptionally rich "pockets". In mica mining, pegmatite 

bodies 6 feet or less in thickness are generally mined from wall 

to wall, but only the mica-bearing shoots are removed from 

thicker bodies.

The color of the mica is fairly uniform throughout any one' 

shoot, but where two or more shoots occur in the same1 pegmatite 

body, the mica of one may differ in color from that of the other. 

The distribution of the mica is irregular, which adds to the uncertainty of mining and to the difficulty of estimating reserves. 

In geologic relations, each mica shoot differs in detail from 

most others, so that a rigid geologic classification of the mica 

deposits would be complex if not impossible.

Shoots of commercially valuable mica occur (1) near contacts 

with metamorphic wall rocks and inclusions (along hanging walls 

more commonly than along footwalls); (2) near constrictions and 

sharp bends ("rolls") in thin pinch-and-swell pegmatite bodies;

10/ Keith, Arthur, U. S. Geol. Survey Geologic Atlas, Mount Mitchell 

folio (No. 12U), pp. 5-6, 1905.
10 STRATEGIC MINERALS INVESTIGATIONS, 1942

(3) near the crests of pipelike or tonguelike bodies; (4) in or 

adjacent to the massive bodies of blue-gray quartz which commonly occur near the centers of pegmatite bodies; and, (5) more 

rarely, in micaceous wall rocks and inclusions partly replaced 

by pegmatite, notably at the Clarissa (87) and Poll Hill (298) 

mine s.

The best mica in the Spruce Pine district (flat and of ruby 

or rum color) is found most abundantly in pegmatite composed 

principally of plagioclase and quartz, or in those parts of more 

heterogeneous bodies that consist mainly of quartz and plagioclase. The mica la associated more consistently with quartz 

than with plagioclase. Pegmatite containing abundant microcline 

and graphic granite rarely contains much muscovite of good quality, except (1) in the few bodies in which lathlike intergrowths 

of muscovite and biotite transect graphic granite, and (2) in 

the many bodies in which mica ticcurs with quartz and plagioclase 

adjacent to, but not intercrystallized with, potash feldspar. 

Pegmatite comparatively rich in biotite is not, in general, rich, 

in muscoviteo Biotite occurs more commonly in pegmatite enclosed in hornblendic wall rocks. In pegmatites containing flat 

mica that is mostly clear, the small proportion of mineralstained mica seems to occur principally near walls and inclusions .

The pegmatite bodies examined in the present study are 

identified by numbers on plate 1. The outstanding characteristics of these bodies, particularly the color of the mica that 

they contain, are summarized in table 2,

In the alphabetical list of mines on plate 1, three symbols 

are used to indicate mines whose production is considered likely 

to contain an appreciable proportion of clear sheet possibly 

suitable for strategic uses. These mines have been selected on 

the composite basis of field examination, value of product, 

reputation among operators and buyers, and, if known, power
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 11

factor. The symbol I indicates mines most of which produce ruby 

or white mica of high quality. Mines marked II also produce 

some mica of high quality, though mostly with different shades 

of rum color. Mines marked. Ill produce mica that apparently is 

of good quality but is green or has a pronounced greenish cast. 

There is some prejudice against clear green mica, but the investigations incidental to this report have not shown that the 

prejudice is well founded. The economic classification implied 

by these symbols cannot of course be infallible or final, and 

further developments will doubtless necessitate some revision.

PROPERTIES AFFECTING THE VALUE OF MUSCOVITE

Muscovite has the approximate formula K(Al,Fe) 2 (Al,Si) 40., 0- 

(OH,F) g , and crystallizes in the monoclinic system. Its principal physical properties have been described and illustrated by

Sterrett.' Only those that serve most to determine its commer-

, 12/ cial value as well as specific uses are described below 0

Cleavage. The outstanding characteristic of muscovite is 

perfect cleavage parallel to the basal pinacoid. Normal, fully 

developed (euhedral) crystals have six faces at right angles to 

the cleavage, but a common variety, known as "A" mica, is incompletely developed. Some faces may fail to develop in a crystal

13/ of either type. A mica crystal is called a block by miners

and buyers.

Undeformed crystals of the normal variety of muscovite can 

be split along the basal cleavage into sheets that have equal 

thicknesses throughout and whose surfaces are essentially plane. 

Hence the normal variety is designated as flat mica. The size 

of a block, and the continuity of the cleavage planes in it,

ll/ Sterrett, D. B., op. clt., pp. 11-lg, pis. 3-S;

I?/ for uses of muscovite, see ffierum, H. 5"., and others, op. clt., pp. 

11-2C

137 The term "hook" is synonymous with "block", but is not used extensively in the southern Appalachians.
Table 2.--Summary of the occurrence of mica in the S

Mine 

numbers

1-61

62-109

110-136

137-157

158-166

167-223

Predominant 

type of 

mica I/

Dark rum.'. .

Ruby and 

rum.

Green, 

stained.

Green and 

rum.

Green "A"; 

some

stained.

Green and 

rum , s ome 

stained.

Subordinate 

types of 

mica

Ruby, green 

"A", white, 

light rum.

Dark rum, 

white.

Mostly shades 

of green 

and brown.

Dark rum, 

ruby.

White ........

Light rum. . . .

Associated minerals 

and rocks

Quartz and plagloclase; pegmatite 

bodies relatively 

thin»

Biotite and microel ine common in 

100-108; otherwise 

mostly quartz and 

plagioclase .

Mica, relatively 

scarce, associated 

with plagioclase; 

micro dine and

graphic granite 

abundant .

Mostly quartz and 

plagioclase; 

mi croc line abundant.

Mostly quartz and 

plagioclase; 

microcline common.

Relative economic importance of 

feldspar

Minor.

Minor. .......

Moderate. ....

Major. .......

Moderate .....

S

o

m

b

D

N

N

N

D

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MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 13

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14 STRATEGIC MINERALS INVESTIGATIONS, 1942

determine the sizes of sheets'that It will yield; and value Increases with size (see table 9). Mica that splits imperfectly 

because the cleavage planes are not continuous through the block 

is termed tanglesheet or gummy. The sheets are trimmed to eliminate marginal imperfections, are split further to specific 

thicknesses, and are die-stamped or cut to shapes required in the 

manufacture of electrical and other apparatus. Thin films known 

as splittings, which are split almost entirely in India, are 

bonded together to form mica board, which may be stamped and 

molded to required forms.

In contrast to the smooth cleavage surfaces of the more valuable flat mica, the cleavage surfaces of "A" mica are uneven because of the presence of fine cleavage imperfections, called 

reeves. The relation of "A" mica to the flat, euhedral variety 

was observed at the Marie mine (16) where a complete six-sided 

crystal, 2,5 Inches in diameter, was divided at intervals of 60° 

by typical "A" reeves into six parts like the pieces of a pie, 

the reeves diverging from the center, and each set bisecting a 

iface of the mica crystal. Almost invariably an "A" mica unit 

develops separately and corresponds to a sixth of a perfect crystal of flat mica. The reeves parallel the long sides, and there 

is no structural feature to form the cross bar of the "A". 

Field evidence indicates that "A" mica is formed later than most 

flat mica.

The extent to which reeves have developed in a crystal of 

"A" mica is the principal measure of its value. If the reeves 

are confined to the margins, "flat A" mica may be trimmed from 

the area between them. Much "A" mica, however, is reeved 

throughout. Mica in which reeving is pronounced occurs commonly 

in crystals that are thinner at the point of the "A" than at the 

blunt end. Such mica is called wedge and is classed as scrap, 

which is ground by wet or dry processes.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 15

Flexibility and elasticity. Sheet muscovite, if free from 

flaws, may be distorted without breaking and returns to its normal planar condition when released. Flexibility is essential 

for some uses, notably in the manufacture of spark plugs for

airplane engines. For making these, films of "cigarette" mica,

14/ 

not exceeding twelve ten-thousandths of an inch in thickness, 

are wrapped around a rodlike spindle a little more than an 

eighth of an inch in diameter. The elasticity of muscovite is 

important where the mineral forms supports for other units in an 

apparatus such as an electric toaster or a radio tube. Common 

flaws affecting these properties are extremely fine cracks having random orientation. Mica with this imperfection is termed 

haircracked, and the term brittle is used to describe mica that 

breaks readily when distorted.

Color.--Color usually can be detected in sheets of muscovite 

a tenth of an inch thick or even less, although thin films appear .to be colorless. The pegmatite bodies of the Spruce Pine 

district contain commercial muscovite of many colors. So far as 

the writers are aware, there has been no systematic study of the 

relation between color and chemical composition, but the differences in hue and intensity of color must reflect some differences of composition. Such a correlation has been found for 

biotite, whose color is dependent on the relative contents 

of iron, magnesia, and titania.

Color terms that are standard in the Spruce Pine district 

are listed below in the order of desirability, and the approximate number of mines whose production of mica is more than 50 

percent unstained is given for each color:

lU/ Wlerum, H. F., and others, op. clt., p. 19.

15/ Hall, A. Jean, The relation between colour and chemical composition 

in the Motites: Am. Mineralogist, vol. 26, pp. 29-3},
16 STRATEGIC MINERALS INVESTIGATIONS, 1942

Mines

Ruby, light pink to light brownish red............... 59

Rum, light brown..................................... 30

White, very pale tone of any color.................. 0 5

Greenish rum, light greenish brown....'............... 9

Water-colored, deep greenish brown................... 19

Green, pale to deep bottle green..................... 14

Slight color variations within crystals are fairly common. 

While some are caused by finely disseminated iron oxide and may 

be classed as staining (see below), many apparently express 

variations in the composition of the mica. Color bands are commonly parallel to the prism faces of the crystal and constitute 

true crystallographic zoning; less commonly, the color varies 

irregularly giving the mica a mottled appearance.

Staining and inclusions.--The value of sheet mica is impaired by stains, mostly of primary origin, on the cleavage surfaces. Secondary organic stains (called vegetable stains) are 

uncommon in the Spruce Pine district, but secondary mineral 

stains, mostly due to infiltrated clay, are common in weathered 

pegmatite.

The primary stains are more serious than the secondary, for 

they persist indefinitely downward. They consist of tiny spots 

of iron oxide, arranged either according to the crystal structure of the mica or at random. The frequency of the spots, or 

"specks", determines whether the mica shall be graded as lightly 

stained, stained, or heavily stained. Heavily stained sheet 

mica is used for Insulation in the commoner electrical appliances, and is frequently called black-stained, black-spotted, or 

electric mica.

The iron-oxide stains are composed of magnetite, hematite, 

and limonite. Magnetite apparently crystallized as inclusions 

during crystallization of the muscovite, and is converted into 

hematite and limonite by weathering. Other inclusions, thicker 

than the iron-oxide films, include crystals of garnet, epidote, 

thulite, zoisite, quartz, apatite, plagioclase, and tourmaline.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 17

The crystals of these minerals grew most readily parallel to the 

cleavage of the mica, so that they are commonly flat. Inclusions interfere with splitting of the mica and must be eliminated in trimming, thus reducing the size of marketable sheets. 

Mica that is intimately intergrown with quartz tends to be brittle.

A little flat mica Is intergrown with biotlte and its alteration product vermiculite. Muscovite Intergrown with the dark 

micas is generally of the desirable ruby color, but it splits 

unevenly; it occurs in many places but not in great quantity. 

Intergrowths of "A" mica and biotite are rare.

The cleavage of mica that has been deformed even slightly, 

or that has been exposed to weathering, may be opened sufficiently to admit air or water. Both are objectionable, but 

water can be removed by drying, and air bubbles can be .eliminated to some extent in splitting the mica.

Natural distortion. The principal effects of distortion of 

mica, resulting from rock movements, are bending and ruling. 

These are most pronounced near faults of minor displacement that 

cut the pegmatite bodies. Such faults are common throughout the 

Spruce Pine district, but are more numerous in the Green Mountain section, north of Burnsvllle, than elsewhere.

Bent mica has curved cleavage and generally has to be ground 

as scrap. Ruled mica has a parting, or secondary cleavage, induced in one or more of three directions 60° apart on the basal 

cleavage. According to Sterrett, 'these directions parallel 

the rays of the pressure figure of muscovite and the reeves of 

"A" mica, and the plane of parting makes an angle of nearly 67° 

with the basal cleavage. Intensity of ruling in flat mica determines the sizes of sheets that may be trimmed from it, and 

mica that is otherwise of highest quality may be ruled 'to such 

an extent that it must be classed as scrap.

l6/ Sterrett, D. B., op. cit., pp. 15-16. 

454759 O - 42 - 4
18 STRATEGIC MINERALS INVESTIGATIONS, 1942

Power factor.--The loss of electrical energy in films of 

sheet mica used as the dielectric in condensers is known as the 

power factor, and is expressed in percent. A low power factor,

generally 0.04 percent or less, is essential in any mica used

17/ for transmitter condensers. Results of tests of muscovite

obtained from domestic mines and from foreign sources have shown 

that the power factor of some domestic mica is comparable with 

that of the best imported material.

TESTS OP SPRUCE PINE MUSCOVITE

The lack of specific information concerning the purposes for 

which sheet mica from the Spruce Pine district has been used 

makes it difficult to evaluate resources with respect to strategic uses and needs. The results, presented in detail on pp. 

19-30, of some tests conducted by the National Bureau of Standards and by two Industrial organizations will serve in some degree to supply this lack.

Measurements of power factor

To determine whether mica having a low power factor is common or uncommon in the Spruce Pine district, the Geological Survey submitted to the National Bureau of Standards samples from 

109 of the district's mica mines and from 15 mines whose principal product is feldspar. Most of these mines have produced 

mica of relatively high value on the local market, but a good 

many of the samples tested were of borderline or inferior quality. The results of the tests are presented in table 3. They 

indicate a close correlation between power factor and physical 

appearance, which therefore provides the geologist and engineer 

with the simplest possible basis for preliminary appraisal of 

quality. Many of the specimens submitted were collected from

12/ Horton, P. ff., Mica: U. S. Bur. Mines Inf. Circ. 6S?2, pp. U3-U5, 

1935.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 19

dumps where they had been exposed to weathering for many years. 

The tests indicate that weathering does not affect the power 

factor so long as the muscovite remains free from haircracks and 

secondary stains.

Mica from 71 of the 109 mica mines has power factors not exceeding 0.04 percent. The specific results gJj/en in the table 

are not to be counted on as applying throughout the respective 

pegmatite bodies, but they indicate approximately the values to 

be expected in the better mica from the mines represented.

The explanatory section of the report of the Bureau of 

Standards on power factors of Spruce Pine mica is quoted in 

full:

This report is submitted in compliance with the request of 

July 10 of Mr. Howard C. Sykes, Consultant on Mica, National 

Defense Commission, and the request of August 3 of the Director 

of the Geological Survey. The samples were submitted on August 

3, 1940.

The majority of the samples were submitted in the form of 

"books", from which sheets 1 to 4 mils thick were split. The 

best-looking pieces were selected, free from cracks, pin holes 

or rock inclusions. Where possible the specimens selected were 

free of visible stains and air bubbles, and the surfaces were 

formed by single cleavage planes. If a specimen about 1 inch 

square could not be obtained, no specimen was prepared; this 

was the case for 18 samples.

The power factor was measured at room temperature for each 

sample at a frequency of 1000 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 lead foil pieces were of two sizes, 7/8-inch 

square and 1^-inch square. The smaller piece did not have to be 

accurately centered above the larger piece. The lead foil 

pieces were attached to the mica using either white petroleum 

Jelly or linseed oil. A small amount of the adhesive was rubbed 

on the mica, and then rubbed off with a piece of chamois, thus 

insuring an extremely small amount of foreign matter. The foil 

was carefully smoothed into place endeavoring to remove all air 

bubbles. The capacitance of the condensers thus prepared ranged 

from about 170 to 800 micromlcrof arads. There were only two or 

three samples under 200 Ai/j-f , the majority being in the range 

from 300 ,to 500

A few experiments were made to determine changes in power 

factor readings as caused by different methods of applying the 

lead foil to the mica specimen. If linseed oil was used without 

care in removing excess oil, the power factor was increased 

about five in the third decimal place. If a minimum amount of 

linseed oil or petroleum jelly was used, the difference in power 

factor was two or three in the third decimal place, depending 

on the adhesive used.
20 STRATEGIC MINERALS INVESTIGATIONS, 1942

Specimens were made up in which small air bubbles were left 

under the electrodes arid the power factor measured. It was observed on three samples that if the air bubbles were removed, 

the power factor was reduced by two to five in the third decimal 

place. It is therefore apparent that the results are not significant to more than ±1 in the second decimal place. The results have accordingly been rounded off at this point.

The power factor tests were made using a type 513-C radiofrequency bridge made by General Radio Company, Cambridge, Mass. 

The standard in terms of which the measurements were made was a 

General Radio type 722-N precision variable air condenser. 

Measurements on three samples were also made using the resist-, 

ance variation method employed in tests reported in this 

Bureau's Research Paper No. 347, "Some Electrical Properties of 

Foreign and Domestic Micas and the Effect of Elevated Temperatures on Mica". Results of tests by the two methods were in 

close agreement.

Tests were made on 18 samples to see if there was any relation between the relative clarity of the mica as indicated by 

its transmission of light and its electrical power factor. A 

red filter was used to differentiate more sharply between ruby 

and green micas. The results indicated no relation between the 

clarity of the mica and its power factor. The clarity data are 

therefore not Included in this report.

Table 3.--Power factors of muscovite from the

Spruce Pine district, North Carolina 

[Tests made by the National Bureau of Standards]

Mine 

No.

1 

4 

15 

19

20

22 

24

25 

28 

35 

40

43 

45 

46 

47

50 

51

52 

54

55

Name of 

mine

Cowcamp ( South) ......

Bluff................

I.... do...... .........

"A" (on Little Elk 

Ridge).

hfi v

I. ...do...............

White Rock...........

Slippery Elm, ........

Hoppey. ..............

Tom Carpenter ........

Honey Waits Wiseman. .

AT rt-pl r»Vi

Alfffld.

JDoublehead. ..........

I. ...do.. .............

{Charlie s Ridge .......

\....do.....t..........

Justice. .............

Branch (on Little 

Henson Creek) . 

Wolf Ridee..... ......

Character of 

specimen

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

Rum, lightly stained. .

"T\o "plf Y*IITTI

Rum, lightly stained. .

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

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

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

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

Puby ..................

Dark rum, lightly 

stained. 

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

T}Q Y»lA YM1TT1 . *

... .do. o .............

Light rum, lightly 

stained.

i/jy.4 A.-

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

Light green. ..........

Rum, heavily stained.. 

Rubv ..................

Power factor 

(percent)

0.05 

.04 

.03 

.10 

.04 

.15

.04 

.04 

.03 

.01 

.03 

.04 

.06

.01 

.08 

.03 

.04 

.07 

.02

.04 

.03 

.04 

.19

.01
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 21

Table 3. Power factors of muscovite Continued

Mine 

No.

59

6P,

66

68

71

81

R3

84

85

88

89

QO

QP

94

QC

96

9R

QQ

100

1 OP

105

107

TOR

1 PI

134:

139

145

146

147

150

151

153

155

162 

164

166

Name of 

mine

Landers. .............

Birch..... ...........

[Little Hawk (head of

\ Henson Creek) . 

I. ...do...:...........

i

TTflwlr

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

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

Haw flat .............

liyjrtqq'tr T? rt /**!/"

I.. ..do.... ...........

Zach Young ...........

f Joe Stevenson. .......

I o ... do ...............

Horton Rock. .........

fCloudland. ...........

1 .... do ...............

Ben Cox. .............

fMllt Wilson. .........

{....do...............

I... .do.. .............

Pannel. ..............

Randall ..............

("Sinkhole .............

I.... do...............

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

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

[Chestnut Branch......

I o... do.... ...........

Jeff Howell. .........

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

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

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

Murphy Rock (on 

Rebels Creek) . 

Glmbel » ............. .

\.... do...............

Jase. ................

Plat Rock. ...........

Miller ..... ..........

4... .do.. .............

[....do........... ....

Da vis ................

fDeer Park No. 2......

l....do...............

"A" (or Brushy Creek) 

Mill Race....... .....

Gushe r Knob ..........

Character of 

specimen

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

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

....do.......'. ........

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

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

ItTM o4"AT*«-f»rtT /"IT^oH"

stained.

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

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

T^Q Y»l/- T*mn

Ruby ................. o

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

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

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

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

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

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

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

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

White... ..............

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

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

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

.. ..do.. ............. o

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

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

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

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

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

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

Rum, lightly stained..

Ruby, lightly stained. 

Ruby, clay-stained....

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

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

Rum. ..................

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

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

r»Y*A ftn

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

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

Light greenish rum. . . . 

Light green, clay

stained. 

Green, lightly

stained.

Power factor 

(percent)

0.04

.08

.03

.01

.03

OP

.04

.04

.04

.47

OP

o?

.02

.01

OP

OP

OP

.01

.08

r)i.

.03

.01

,,04

.01

o?

o?

.06

.01

.01

.01r\-i

/-\o

.06

.01

.04

O?

.04

o^

.04

.02

*^O

.01

.01

no

OQ

r)-z

.01

.02

.01

n^

.02/TZ

.02

.11

.01
22 STRATEGIC MINERALS INVESTIGATIONS, 1942

Table 3.--Power factors of muscovlte--Continued 

Mine 

No.

166

174

1 QP

T OQ

T QQ

208

210

211

PI 4.

p^n

P^R

JWfi

237

?,?>9

P4.fi

P4-7

pAQ

P..SO

P,55

P7 1*

P76

P77

282

PR 3

S?R5

287

288

289

PQ1

pop

PQ6

PQfl

pQQ

300

TOP

Name of 

mine

Gusher Knob. .........

\A/ 1 QArtifiY"!

I.... do...............

"Hp o LTA

Miller...... .........

Guy. .................

T^T*n W'hfl T*

"P/^-f- o a 4*

Hootowl. .............

JBarger. ..............

I.... do...... .........

fBuckeye (west of

i Boonf ord) . 

I .... do ...............

Branch (west of

Boonf ord) . 

Hector. ..............

Charles Robinson.....

Tolley Bend. .........

Pr»A Q "1 A v

An£tli.n« o

flooCTT*rt f*lf

Andy Hall ............

Bee Ridge (North) ....

Bee Ridge (South)....

Charley Young. .......

Bittner.. ............

Griffin..............

of Shoal Creek) . 

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

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

I .... do ...............

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

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

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

\....do...... .........

Flukens Ridge (at

Newdale) .

[Poll Hill............

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

, ....dp...............

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

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

fGibbs................

I.... do...............

Hilliard. .... ........

River) .

Character of 

specimen

stained. '

nT»AAl*l VlAQT7"1T"Tr

stained.

Dark green, heavily

stained. 

Rum, clay-stained.....

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

stained.

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

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

t...do................

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

.-...do... .............

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

Light green. ..........

Rum, lightly stained..

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

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

Ruby. ...... i ..........

... .do. .. o ............

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

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

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

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

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

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

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

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

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

Wh1 -I- A

Rum. ..................

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

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

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

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

.. ..do...... oo...

Rum, lightly stained..

Ruby ................0.

/T.T»£* ov"* a 4" Q 1 nA f^

Power factor 

(percent)

0.02

2.00

.02

.16

1.70

.IP

O?

.03

OQ

O?

.20

.01

.04

OQ

.01

.02

.04

.05

.01

.01

O?

.01

.01

.05

.O?

OP

.01

OP

.10

.02

.O?

OP

(-) *

.03

.03

' .02

OP

o?

.01

.07

.31

.02

.03

.02

.01

.02

.03

.09

.06

.02

.07
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C, 23

Table 3. Power factors of muacovite Continued

Mine 

No.

 zn-z

304

307

 IT 1

 ZT -Z

314

 ZO-I

 ZO7

330

336

339

340

344.

345

34fi

348

350

354

355

356 357-

358

1.HO

l-fiQ

374

ft

C 

o

o 

am

4^

C

-P

(D 

ft

0

£H

Name of 

mine

Edge .................

Wilt Young ...........

Bailey Mountain 

(group) . 

... o do ...............

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

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

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

o ... do ...............

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

Myra Gibbs. ..........

Big Gibbs... .........

Gaston McDowell. . . . . ;

No. 6. 

George Young. ........

W1 "IrJrflt

f Josh Young ...........

' ....do...............

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

Sally Knob. ..........

\. ...do.... ...........

Georges Pork. ........

(Ray..................

to... do...............

Willies Shanty. ......

A trl A a C* T*A fllr

fS. W. Presley...

4 .... do ...............

[....do...............

Plem McPeters ........

Cattail.. ............

Westall (on Colbert

Ridge).

Brown (1.5 ml. NWo

of Mt. Mitchell). 

Blevins (0.2 mi. N.

of Zach Young 

mine ) . 

Buck Hill Rock (S. 

slope Buck Hill 

Mtn. ) . ' 

iChet McKinney (S. of

Carson Rock mine). 

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

McKinney (E. of

Cattail mine) .

of Dugger mine) .

Character of 

specimen

Rum, from Black Dixie. 

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

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

Shake rig . 

Rum, from Sleepy

Hollow. 

Rum, from Irby Cut....

Rum, from Old Owlie...

unknown .

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

Rum. ..'................

Greenish rum. .........

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

Green. ................

stained.

Green. ................

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

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

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

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

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

Ruby, stained. ........

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

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

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

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

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

....do...........;....

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

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

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

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

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

Rum, lightly stained. . 

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

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

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

Power factqr 

(percent)

0.04

.06

.02 

.06

.05

no

n 1*,

.01

.02

.01

.10(T*.

.OP

OP

.01

.01

..01

.03

2.00

.04

.06

.01

.02

.05

.07

OP

.01

.01

fip

.05

.02

.01

.03ri-z

.01

.02

.02

.03

.0?

.03

.08 

.03

.04

.01

OP
24 STRATEGIC MINERALS INVESTIGATIONS, 1942

Table 3.--Power factors of muscovite--Continued

Mine 

No.

-P ft

O CO c a

n c 

-P 0

O 

<D £

ft 5 

ra o

0X3

k <n 

f^

Name of 

mine

[Ledford (on Cane

j Creek). 

I. . . .do.... ...........

"Elf^wnT*H^ Q r* Y*fl T^ ml f* Q

mine (near 

Newdale ) .' 

{Sheehan (1 ml. N. of

Micaville). 

.... do ..... o .........

Character of 

specimen

.... do o ...............

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

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

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

Power factor 

(percent)

0.02

ri-z

.06

.01

.01

Results of the tests of Spruce Pine muscovite, shown in 

table 3, are summarized by Mr. Hall in table 4, to show the distribution of the power-factor values.

Table 4. Distribution of power-factor values of Spruce 

Pine muscovite, summarized from table 3

Range of power factor 

(percent)

0 - 0.014 .. ............................

.015 - .025.... ..........................

.02e ' .034. ..............................

; .035 - .045 ..............................

ClAr- Ctf\ A

.055 - .085. .............................

.086 - ,114 ..............................

Total ............................'......

Number of specimens 

tested

 ZQ

48

31

?1

PI

17

Q

10

196

The measurement's of power factor listed in table 4 were, made 

in August 1940. Mr. Hal-1 remeasured 10 of the specimens in December 1940, and he found a decrease in power factor in each 

sample except one. He attributed the decrease to the drying out 

of the specimens from August to December. Comparative results 

are shown in table 5.

Table 5. Comparative results of power-factor 

measurements made in August and December 1940

Mine 

No.

24 

45 

94 

100 

199 

236

Name of 

mine

Elk ...............

Aldrich...... .........

Cloudland. ............

Randall. ..............

T^A Q I^A

Buckeye (west of

Power factor 

(percent)

August

0.04 

.08 

.08 

.06 

.12

.09

December

0.03 

.03 

.06 

.03 

.10

.08

Change in power 

factor 

(percent)

-0.01 

-.05 

-.02 

-.03 

-.02

-.01
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 25

Table 5.--Comparative results of power-factor measurements 

made in August and December 1940 Continued

Mine 

No.

299 

307

Name of 

mine

Glbbs.

/Bailey

1 rtn

Power factor 

(percent)

August

0.06 

.02 

.05 

.02

December

0.04 

.01 

.02 

.02

Change in power 

factor 

(percent)

-0.02 

-.01 

-.03 

0

Teats to determine utility in condensers

The results obtained from the tests conducted by the National Bureau of Standards indicate that sheet mica of sufficiently 

low power factor for use in condensers probably occurs, though 

in unknown quantity, in many of the mines in the Spruce Pine 

district. In order to obtain more definite information regarding utility, relatively small samples were collected from six 

mines that were being operated in May 1941, and from four mines 

also in operation at that time in North Carolina but outside the 

Spruce Pine district. The .10 samples had to be taken from the 

limited stocks of mica then available, and at least 4 of them 

were considered to be slightly inferior in quality'to the best 

mica obtainable from the respective mines. The power factors of 

mica from the six mines in the Spruce Pine district, as determined by the Bureau of Standards, ranged from 0.01 to 0.08 

percent.

Under an arrangement made by Mr. Paul M. Tyler of the Bureau 

of Mines, United States Department of the Interior, five of the 

samples were sent to the Scintilla Magneto Division of the Bendix Aviation Corporation, at Sidney, New York, and five to the 

R. C. A. Manufacturing Co., Inc., at Camden, New Jersey. The 

laboratory staffs of these companies processed the mica of each 

sample separately, with the results given below. It will be 

noted that the inadequacy of the samples for exhaustive tests is 

emphasized in the report of each company. The unfavorable results obtained on mica from 2 out of the 10»mines might possibly
26 STRATEGIC MINERALS INVESTIGATIONS, 1.942

be due to the unsatisfactory way in which the samples were 

taken. In order, therefore, to avert the possibly unjust inference that these two mines cannot become sources of condenser 

mica, it was considered inadvisable to identify the individual 

mines further than by indicating whether they are within or outside of the Spruce Pine district.

Tests made by the Scintilla Magneto Division, Bendix 

Aviation Corporation, Sidney, N. Y.»

Fabrication of mica.--

Table 6. Table showing relation by weight of finished 

condenser films to raw mica

Mine

A ?/. .....

R P /

r p /

D. ..........

Weight of raw 

mica in sample

1 Ib. 10.0 ozo 

1 Ib. 12.0 oz. 

11.5 ozo 

1 Ib. 5.5 oz. 

1 Ib. 1.0 oz.

Approximate average for Ind

Weight of 

condenser

finished 

films I/

2.75 oz. 

3.50 oz» 

2.25 oz. 

3.00 oz. 

3.25 oz.

U Tttl f* n

Relation of film 

weight to raw 

weight (percent)

10 

12 

19 

14 

19

25

I/ Dimensions of the films in inches: 1.370 ± 0.010 by 1.370 ± 0.010 by 

0.0009 to O.OOlU.

2j Spruce Pine district.

Comments by Scintilla. 

(1) The dielectric strength, power factor, and dielectric 

constant of the various samples are acceptable for condenser 

splittings,

(2) All samples were free splitting, and no particular difficulty was encountered during the process of manufacturing.

(3) The percentage net weight is only partly indicative of 

the suitability of the various samples, owing to the fact that 

the size of the sheets was not uniform.

(4) The variation in color of the various samples submitted 

was not indicative of the suitability of the various micas for 

the Intended purpose.

(5) Prom all indications obtained during, the processing of 

the above samples, the various micas can be used for condenser 

films, although the small quantity of raw mica submitted limited 

us somewhat in our investigation.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 27 

Tests made by the R. C. A. Manufacturing Co., Inc., Camden, N. J.

Descriptions and fabrication of mica. 

Mine F (Spruce Pine district)

Description of sample: Color very light green. Very 

soft. Many air inclusions and a few foreign inclusions. 

Very scaly in splitting. Only occasional pieces flat.

Weights:

Sample................................ 2 IDS. 9.00 oz.

Scrap from splitting.................. 3.75 oz.

Scrap from cutting.................... 1 Ib. 4.30 oz.

Reject films.......................... 7.75 oz.

Good films ............................ 9.25 oz.

. Relation of film weight to raw

weight (percent).................... 22.5

Mine G (Spruce Pine district)

Description of sample: Color a great deal like ruby but 

darker and somewhat more brownish. Poorly trimmed blocks 

split poorly. Well trimmed blocks split very well, and are 

reasonably flat and clear. Cracks often run. in far enough 

from the edges to ruin otherwise good blocks. Harder than 

India ruby.

Weights:

Sample................................ 1 Ib. 15..80 oz.

Scrap from splitting.................. 1.90 oz.

Scrap from cutting.................... 20.00 oz.

Re je ct films.......................... 1.3 bz.

Good films............................ 8.60 oz.

Relation of film weight to raw

weight (percent).................... 27.0

Mine H (Spruce Pine district)

Description of sample: Color same as G. Many quartz 

inclusions. Splits fairly well when well trimmed, but most 

of sample poorly trimmed.. Much air. Many cracks. Hard.

This sample showed such a high power factor at 1000 

kc., by preliminary bridge measurement, that no further 

work was done on it.

Mine I

Description of sample: Color greyish brown with slight 

ruby tinge. Very poorly trimmed. Many quartz and other 

inclusions and holes. Surfaces fairly flat, splits well. 

Very hard.

Weights:

Sample................................ 1 Ib. 8.50 oz.

Scrap from splitting.................. 1.50 oz.

Scrap from cutting.................... 14.00 oz.

Re je ct films.......................... 1.50 oz.

Good films............................ 7.50 oz.

Relation of film weight to raw

weight (percent).................... 30.6
28 STRATEGIC MINERALS INVESTIGATIONS, 1942

Mine J

Description of sample: Color similar to I but with 

yellowish shade in'place of ruby, giving lighter brownVery irregular surface, very scaly and splits poorly. 

Numerous air and mineral inclusions. Very poor mica in 

appearance.

Weights:

Sample ...................................... 10.70 oz.

Scrap from splitting........................ .70 oz.

Scrap from cutting.......................... 5.80 oz.

Reject films................................. .40 oz.

Good films.................................. 3.80 oz.

Relation of film weight to raw weight

(percent)................................. 35.0

Results of electrical tests. Silvered mica test capacitors 

(condensers) were built from the mica of each sample using the 

film thickness of which there was the greatest quantity in all 

samples. The samples were prepared by vaporizing silver on 

cleaned pieces, with a one-eighth inch margin. In some samples 

there was enough mica for only one capacitor, and the tests on 

these samples cannot be given much weight. Some India ruby mica 

was tested at the- same time for comparison.

The electrical characteristics of each capacitor were determined, and they are listed below. Whenever there was a question about the results of a measurement, the tests were repeated 

on one or two extra pieces of mica. For load tests, each capacitor was run at its standard current rating at 1,000 and at 

3,000 kc. until temperature stability was reached, as indicated 

by a spirit thermometer attached to the clamp. The results are 

tabulated in degrees Centigrade rise per KVA input, averaged 

over all capacitors tested from each sample.

Comments by R.C.A. 

(1) The preparation of the mica in these samples is considerably below the standard set by suppliers of India ruby 

mica. The physical quality of the mica is also below that of 

India ruby.

(2) The yield of finished films is not much more than half 

that of India mica, which is about 50 percent. Much of this 

loss is due to poor trimming by the supplier, leaving much waste 

material that should not reach the fabricator.
Table 7.--Results of electrical tests by 

Mine

PI/.

G I/.

H I/o

I....

J. . ..

India 

ruby.

Quantity 

of mica 

tested 

(pieces)

3

6

6

3

5 

3

Average 

capacity 

(Mmfd.)

520.4

532.1

537.8

533.4

531.5 

532.0

Area 

(sq. 

cm. )

8.46

9.31

8.27

8.70

9.36 

7.93

Thickness 

(cm.)

0.01023

.0111

.0098

.00998

.01075 

.00971

Power factors at 

1.000 kc. (percent)

Highest

0.019

.035

.0467

.0241

.0261 

.0141

Lowest

0.0142

.00602

.0043

.0172

.005 

.00612

Average

0.0165

.0160

.0311

.0203

.0159 

.0106

Dielectric 

constant

7.11

7.17

7.19

6.89

6.87 

7.34

L

1

No

\J Spruce Pine district

Flashover test: All samples were tested on D.C., and flashed ov

the mica dielectric was not punctured in any sample.
30 STRATEGIC MINERALS INVESTIGATIONS, 1942

(3) Of the samples tested, that from mine J indicates the 

highest loss under load tests nearly twice that of India mica. 

The other three appear to be low enough to be reasonable substitutes for India mica.

(4) The dielectric strength of all samples is apparently 

equivalent to that of India mica.

MINING AND MARKETING 

History of mining

The early history of muscovite mining in the Spruce Pine

18/ district has been summarized by Sterrett. ' Weathered surficial

portions of several pegmatite bodies were mined by American 

Indians before the region was settled by white men, but modern 

mining began in 1868. There was demand only for sheet mica, 

used principally as stove windows, until about 1893, when the 

grinding of scrap mica was begun. This provided an outlet for 

mica whose irregular cleavage makes it unfit for punch or sheet, 

and the demand for ground mica increased steadily until some 

mines were operated for scrap mica alone.

Sheet mica was first mined in weathered, easily excavated 

pegmatite, where large blocks were found at the surface. When 

hard rock was encountered, mining was continued by hand drilling 

until the inadequate pumping facilities could no longer handle 

the water. Improvement of equipment and growing demand for all 

grades of mica caused some of the better mines to become relatively large. The largest mines in the district are feldspar 

mines, most of which produce mica as a byproduct. The following 

are among the largest of the mica mines:

19 Meadow................... Series of stopes 900 feet long.

24 Elk...o.................. Series of stopes 900 feet long.

51 Charlies Ridge........... 500-foot incline.

81 Hawk..........o.......... Tunnel and stopes 800 feet long.

87 Clarissa...........o..... Series of shafts 450 feet long,

maximum depth 475 feet. 

105 Sinkhole................. Series of interconnecting

shafts, 1,100 feet long. 

296 Fannie Gouge............. 850-foot incline.

298 Poll Hill.o......o....... 850-foot incline.

299 Gibbs.................... 500-foot incline.

IS/ Sterrett, D. B., op. clt., pp. 167-168.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 31

Of 219 mica mines examined, 50 were being worked on a small 

scale during the period from November 1939 to the end of May 

1940. Five of these mines employed more than 4 men each; the 

other 45 were operated intermittently by 2 or 3 men each. The 

remaining 169 mines were in various stages of inaccessibility 

because of flooding and caving. By May 1941, there had been 

considerable revival of mining, and some of the largest of the 

mines had been reopened.

One of the principal difficulties encountered in the study 

of domestic mica mining is that of intermittent operation, which 

can be caused by fluctuating prices, by legal difficulties, and 

by the erratic distribution of the mica. Table 8 shows, as examples, the intermittency of operation in five mines during 

periods for which records of production are available. The 

table indicates that the known or estimated output of a mine 

over a long period of years is commonly the result of actual 

mining during a small fraction of that time, and this fraction 

usually is the sum of still smaller fractions. Such frequent 

alternations of mining and abandonment must of course add considerably to mining costs.

Table 8«--Table showing intermittent operation of mica 

mines in the Spruce Pine district

Mine 

No.

PI 4.

P4.Q

289 

PQfl

345

Name of 

mine

PY»«Q*I £t-rr

Little Zeph Young... 

Poll Hill...........

Murphy Rock (on 

Crabtree Creek) . . .

Period of 

recorded 

production

1 Ql 7 ^^

1 QPP-AO

1926-38 

i en 7-^R

1930-38

Approximate 

percentage 

of full-time 

operation

27

Pfi

20

 XQ

24

Calculated 

actual working 

time (years)

4.4

4.5

2.5 

8.2

2.1

Grading and prices

Domestic raw mica is divided commercially into three 

classes: sheet, punch, and scrap. Sheet and punch consist of 

flat and "flat A" mica that can be stamped, trimmed, or fabri-
32

catedo In the Spruce Pine district, the terms "No. 1", "No. 2", 

and "No. 3" are used to designate general quality. "No. 1" is 

domestic clear mica, free of mineral inclusions, and corresponds 

approximately to the Indian and A.S.T.M. grades "clear", "clear 

and slightly stained", "fair-stained", and some "good-stained". 

"No. 2" is less perfect because of waviness, clay staining, or 

minor iron-oxide staining, and corresponds to the Indian 

"stained" and possibly some Indian "black-stained". "No. 3" is 

heavily stained with magnetite or hematite and corresponds to 

most of the Indian "black-stained or spotted" mica.

According to common usage, therefore, clear domestic mica 

includes not only sheet that is clear according to the Indian 

classification, but "fair-stained" and "good-stained" as well, 

and the term "clear" is used in this report in the same broad 

sense.

Sheet mica is graded according to size as well as quality. 

The general range of prices of mica locally classed as clear 

trimmed sheet, from 1917 to 1940, is shown In table 9. Prices 

fluctuate according to demand, and are currently at the maximum 

level. Sizes larger than 8 by 10 inches are rare..

Table 9.--Price range of clear sheet mica In the Spruce 

Pine district, 1917-40

Size 

(Inches)

1| x 2 

2x2 

2x3 

3x3 

3x4

Price range 

(per pound)

$0»15 - 0.60 

.30 - loOO 

.45 - 1.40 

.60 - 2.00 

»80 - 2.30

Size 

(Inches)

3x5 

4x6 

6x8 

8 x 10

Price range 

(per pound)

$1.00 - 2.65 

1.75 - 3.60 

2.25 - 7.00 

3.50 - 11.00

Small sheet mica is classed as punch mica. Specifically, 

punch includes stained mica smaller than 2 inches square, but 

more than 1^ inches in diameter, and clear mica smaller than 1 

x 2 inches, but of greater diameter than 1^ inches. Its value 

has ranged from 3 to 12jg- cents per pound over a long period of 

years. /
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 33

Scrap mica, which is suitable only to be ground, comprises 

strongly reeved "A" mica, ruled and bent flat mica, trimmings 

from the manufacture of sheet and punch, and relatively finegrained muscovite recovered from decomposed pegmatite and mica 

schist. Prices for scrap mica have ranged mostly from $10 to 

$20 per ton.

Production

The Spruce Pine district has been more or less consistently 

the principal producing area not only of North Carolina but of 

the United States. During 1929 and 1930, it is reported to

have produced more than 85 percent of the State's total produc19/ tion of sheet mica. ' This probably is higher than the all-time

average, which may be estimated conservatively at about 65 percent. The recorded production of clear and stained sheet mica, 

including punch, from North Carolina is shown in table 10. The 

production of scrap mica is not listed because the amount obtained from mica-bearing pegmatite has been obscured during recent years by scrap derived from mines in clay, decomposed peg20/ matite, and mica schist. The total production of scrap mica

from North Carolina far exceeds ,in volume that of sheet and 

punch combined, and it has exceeded sheet and punch in value in 

most years since 1925.

Table 10.--Recorded production of sheet and punch mica from 

North Carolina, compared with total for the United States, including North Carolina I/

Period

1868-81 

1880 

1881

Amount ( i

North Carolina

400,000 

Unrecorded 

.... do ... .

Dounds)

United States

Unrecorded 

81,669 

100,000

Value

North Carolina

$800,000 

Unrecorded 

... .do....

United States

Unrecorded 

$127,825 

250,000.

\J Figures from U. S. Geol. Survey Ann. Repts. 18-21, 1397-1901; Mineral 

Resources U. S., 1825-1931; and Minerals Yearbook, 1932-Ul.

19/ Urban, H. M., Mica-mining methods, costs, and recoveries at the No. 

10 and No. 21 mines of the Spruce Pine Mica Co., Spruce Pine, N. C.: U. S. 

Bur. Mines Inf. Circ. 66l6, p. 2, 1932.

20/ Tyler, P, M., and Warner. K. G., Mica: Minerals Yearbook, pp. 1360-

1361,
34 STRATEGIC. MINERALS INVESTIGATIONS, 1942

Table 1Q. Recorded production of sheet and punch 

mica--Continued

Period

1882

1883

1884

1885

1886

1887

1888

1889

1890

1891

1892

1893

1894

1895

1896

1897

1898

1899

1900

1901

1902

1903

1904

1905

1906

1907

1908

1909

1910

1911

1912

1913

1914

1915

1916

1917

1918

1919

1920

1921

1922

1923

1924

1925

1926

1927

1928

1929

1930

1931

1932

1933

1934

1935

1936

1937

1938

1939

1940

Amount ( p ound s )

North Carolina

60,000

68,400

100,000

60,000

24,000

50,000

20,000

Unrecorded

....do....

....do....

... .do....

....do....

....do....

... .do....

....do....

65,225

84,687

85,707

107,255

266,160

303,816

Unrecorded

610,121

742,875

800,440

645,221

599,234

1,296,274

455,020

454,653

489,599

803,462

274,121

281,074

546,553

643,476

941,200

1,021,306

1,084,946

230,532

544,495

1,130,283

597,385

592,478

700,313

665,360

777,395

894,200

749,074

389,426

127,696

162,672

293,381

512,590

730,446

1,044,328

632,646

401,170

1,002,646

United States

100,000

114,000

147,410

92 ,000

40,000

70,500

48,000

49,500

60,000

75,000

75,000

66,971

35,943

84,408

Unrecorded

82,676

129,520

108,570

456,283

360,060

373,266

619,600

668,358

924,875

1,423,100

1,060,182

972,964

1,809,582

2,476,190

1,887,201

845,483

1,700,677

556,933

553,821

865,863

1,276,533

1,644,200

1,545,709

1,683,480

741,845

1,077,968

2,063,179

1,460,897

1,793,865

2,172,159

1,512,492

1,681,777

2,035,128

1,465,485

962,953

338,997

364,540

583,528

936,633

1,319,233

1,694., 538

939,507

813,708

1,625,437

Value

North Carolina

$150,000

171,000

253,000

105,000

42,000

87,500

Unrecorded

....do....

....do....

....do....

....do....

....do....

.. ..do....

....do....

56,802

Unrecorded

. ...do....

....do....

.... do ....

.... do ....

65,419

Unrecorded

100,724

117,732

205,756

209,956

114,540

122,246

193,223

187,501

219,874

230,674

171,370

266,650

380,700

543,207

460,450

331,498

405,654

51,851

119,767

188>317

108,656

105,376

150,362

114,514

129,706

150,293

112,451

51,657

18,322

21,107

38,674

77,598

119,653

218,176

87,879

69,344

218,154

United States

$250,000

285,000

368,525

161,000

70,000

142,250

70,000

50,000

75,000

100,000

100,000

88,929

Unrecorded

50,381

65,441

80,774

103,534

70,587

92,758

98,859

83,843

118,088

109,462

160,732

252,248

349,311

234,021

234,482

283,832

310,254

282,823

353,517

278,540

378,259

524,485

753,874

731,810

483,567

546,972

118,513

194,301

311,180

212,035

321,962

400,184

212,482

230,956

286,321

177,307

111,830

45,882

53,179

90,268

191,150

203,879

285,244

139,333

138,963

291,685
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 35

Most of the mica mined in the district is sold to local buyers. Fairly complete records of production for the year 1938 

show that 528 producers made 1,380 sales of mica, or an average 

of 2o6 sales each during the year. Eighty percent of these 

sales were of small lots, each less than $25 in value, obtained 

from part-time mining by hand methods, but these small lots accounted for only 14 percent of the year's total production of 

sheet mica (both clear and stained). The bulk of the sheet 

mica, therefore, was produced from a few relatively large mines,.

Complete records of production could be obtained for only 

3 out of a total of approximately 225 mica mines. As these have 

been opened since 1935, the difficulty of reconstructing production histories is obvious. Incomplete records, extending as far 

back as 1917, have been obtained also for 100 mica mines, and 

for the mica output of 27 feldspar mines. The recorded production of each of these 130 mines has been analyzed, and some of 

the results are shown in table 11. In assembling production 

data, attention was focused on relatively clear sheet mica, 

which has been the main product of most of the mines listed in 

the table. No special attempt was made to obtain complete figures for large producers of stained mica, such as the Meadow 

and Hootowl mines, and records pertaining to the output of scrap 

mica from individual mines are too fragmentary to be included. 

Scrap generally constitutes 65 to 90 percent, by volume, of the 

output of a mine.

Recorded production of clear sheet from the mines listed in 

table 11 has been combined to determine the size range of aggregate production, and the results are shown in table 12, together 

with values. The percentages of the different sizes of clear 

sheet are based oh nearly, half a million pounds of mica, most 

of which is classed as among the best produced in the district, 

and should be of considerable value in estimating the size 

range of future production of sheet mica from Spruce Pine.
36 STRATEGIC MINERALS INVESTIGATIONS, 1942

Table 12.--Analysis of aggregate recorded production of sheet 

mica from 130 mines in the Spruce Pine district, 1917-40

Sheet and punch.

Quantity 

(pounds)

605,880

1 ' 797 * 774

2,403,574

Percent 

of total 

quantity

OC t-,

74.8

100.0

Value

&AQ'*: RRO

105,013

588,565

Percent 

of total 

value

GO O

17.8

100 = 0

Average 

value 

per pound

$0.789

.058

.245

Sheet mica

Size

8 x 10...................

6 x 8.... ...............

4 x 6.. .................

3 -v R

3 x 4. ..................

3 x 3.... ...............

2 x 3 ...................

O y O

~\ TT P

TTv-|rt"l Q a a 1 f ^ f*r{

ryi,^4- Q "1 «

Clear

Pounds

1,070 

3,155 

16,434 

29,572 

23,489 

35,524 

97,273 

99,117 

161,418 

7,573

474,625

Percent 

of total

0.225 

.664 

3.463 

6.230 

4.949 

7.484 

20.495 

20.885 

34 o 007 

1.598

100.000

Stained

Pounds

95 

720 

5,271 

12,992 

9,015 

13,605 

39,853 

47,772

1,852

131,175

Percent 

of total

0.072 

.549 

. 4.018 

9.902 

6.872 

10.375 

30.378 

36.415

1.419

100.000

FUTURE POSSIBILITIES

The erratic distribution of mica in pegmatite bodies of the 

Spruce Pine district makes it impossible to judge the economic 

possibilities of any single working face or outcrop, and it precludes specific estimates of reserves. It is possible to sample 

qualitatively, but not quantitatively. Theoretically, any pegmatite body proved by previous mining to contain mica of profitable quantity and quality may be regarded as a potential source 

of further production. Practically, however, this generalization is inapplicable for several reasons, chief among which is 

the lack of any known method of prospecting to block out valuable parts of the body. Diamond drilling might locate micabearing pegmatite, but is unlikely to provide any assurance that 

the mica crystals would be of commercial size and quality. 

Prospecting of this type might, in a few places where thin pegmatite bodies have been productive, find minable parallel bodies.
MUSCOVITE IN THE SPRUCE PINE DISTRICT, N. C. 37

Renewal of activity in abandoned mines, therefore, depends 

almost entirely on stimulation provided by market conditions, 

with the result that prospecting and mining merge into a single, 

economically hazardous undertaking. Operators will not invest 

in the machinery necessary to develop mines adequately without 

some assurance that prices will remain at a level that will 

justify the risk.

Production of sheet mica from North Carolina from 1924 

through 1940, was 2,051,478 pounds, excluding 8,221,728 pounds 

of punch mica. At least 75 percent of the sheet, or 1,538,609 

pounds, came from the Spruce Pine district, and about half of 

this amount was stained. The remainder, 769,305 pounds, is approximately the Spruce Pine district's production of clear 

sheet, larger than punch, during the 17-year period. The resulting average of 45,253 pounds per year includes the effects 

of variable market conditions, and may represent a rough average 

to be expected in the future if market conditions fluctuate in 

the same way. The results of the tests by the Bureau of Standards, listed above, indicate that much of the Spruce Pine mica 

has power factors as low as the best imported mica.

The computed average yearly production during* the period 

1924-40 was attained without coordinated planning and, in many 

cases, without proper equipment. It is known from the past 

history of the Spruce Pine district that rise in prices will 

not, of itself, affect production capacity quickly, nor permit 

attainment of approximate full capacity before a succeeding decline. There is little doubt that production of relatively 

clear sheet mica can be stimulated to an average figure possibly 

two to three times that of. the years 1924-40, by (1) concentrating principally on mines that produce the most desirable mica, 

of which there are 70 or more, and by (2) promoting simultaneous 

operation in order to keep total production fairly uniform even 

though the output of individual mines may fluctuate. The data
38 STRATEGIC MINERALS INVESTIGATIONS, 1942

presented in table 11 provide a preliminary basis for estimating 

the Individual production of most of the mines that would be involved in a systematic program, and7 those presented in table 12 

may be used to estimate aggregate o''production.