White Clays of 

Pennsylvania

GEOLOGICAL SURVEY BULLETIN 1558-D

White Clays of 

Pennsylvania

By JOHN W. HOSTERMAN

CONTRIBUTIONS TO THE GEOLOGY OF MINERAL DEPOSITS

GEOLOGICAL SURVEY BULLETIN 1558-D

Geology and geologic setting of 

white clays

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1984
DEPARTMENT OF THE INTERIOR 

WILLIAM P. CLARK, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Hosterman, John W. (John Wallace), 1923-

White clays of Pennsylvania.

(Contributions to the geology of mineral deposits)

(U.S. Geological Survey bulletin ; 1558D)

Bibliography: p.

Supt. of Docs, no.: 119.3:1558D

1. Kaolin Pennsylvania. I. Title. II. Series. III. Series: Geological Survey

bulletin ; 1558D. 

QE75.B9 no. 1558D 557.3s [553.6T09748] 83-600354 [QE471.3]

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Page

Abstract................................................................................................................................ Dl

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

Methods of investigation.................................................................................................... 3

Acknowledgments .............................................................................................................. 5

Clay deposits near Kunkletown and Saylorsburg, Monroe County ...................... 5

Location and history............................................................................................... 5

Geology............................................................................................................................ 6

Composition ................................................................................................................. 7

Narvon clay pit, Lancaster County ............................................................................... 13

Clay pit near Dillsburg, York County......................................................................... 13

Clay deposits near Mount Holly Springs, Cumberland County.............................. 15

Location and history................................................................................................... 15

Geology........................................................................................................................... 15

Composition .................................................................................................................. 19

Clay deposits in the Gatesburg Formation of Centre, Blair, Huntingdon,

and Bedford Counties ............................................................................................ 22

Location and history.................................................................................................. 22

Geology.......................................................................................................................... 24

Composition ................................................................................................................. 25

Clay deposits in the Oriskany Group of Huntingdon County ................................. 27

Origin of the white clay deposits ................................................................................... 32

Conclusions............................................................................................................................ 37

References cited ................................................................................................................ 37

ILLUSTRATIONS

Page

FIGURE 1. Index map showing location of white clay deposits in

Pennsylvania ............................................................................................. D2

2. Geologic map of the Universal Atlas Cement Co. clay pits

on Chestnut Ridge ...................................................................................... 9

3. Clay pit of the Philadelphia Clay Co. at Toland showing location

of auger holes................................................................................................ 18

4. Map showing outcrop belt of the Gatesburg Formation ...................... 23

5. Clay mine in the Stormstown pit. Centre County .................................. 26

6. Map showing the location of auger holes near the Oreminea

1 and Oreminea 2 clay pits...................................................................... 33

III
IV CONTENTS

TABLES

Page

TABLE 1. Chemical and mineralogical composition of residual silty clay

from the Atlas clay pits near Kunkletown, Monroe County.............. DIG

2. Chemical and mineralogical composition of residual clayey silt

from the Narvon pit, Lancaster County.................................................. H

3. Chemical and mineralogical composition of residual clayey silt

from the pit near Dillsburg, York County.............................................. 16

4. Chemical and mineralogical composition of white clay from two 

auger holes drilled at the Toland clay pit near Mount Holly 

Springs, Cumberland County .................................................................... 20

5. Average composition of the clay and enclosed rocks at the

Toland pit........................................................................................................ 21

6. Chemical and mineralogical composition of white clay from the

Stormstown pit, Centre County ................................................................ 28

7. Chemical and mineralogical composition of white silty clay from

the Oreminea area, Blair County.............................................................. 30

8. Mineralogical composition of clay from five clay pits in the Gatesburg Formation, Centre, Huntingdon, and Blair Counties .............. 32

9. Mineralogical composition of clay from three clay pits in the

Oriskany Group, Huntingdon County...................................................... 32
CONTRIBUTIONS TO THE GEOLOGY OF MINERAL DEPOSITS

WHITE CLAYS OF PENNSYLVANIA

By JOHN W. HOSTERMAN

ABSTRACT

The white clays of Pennsylvania are composed chiefly of kaolinite and various 

amounts of illite. Most of the white clays are silty and a few are sandy. Quartz or chert 

is the only nonclay mineral in the whitest material; goethite is also present in the 

colored samples high in iron. The average alumina content is slightly more than 20 

percent in samples from three clay pits and less than 15 percent in samples from five 

clay pits. The white clay deposits are found in eastern, south-central, and central 

Pennsylvania. They occur in rocks of the Appalachian basin that range in age from 

Cambrian to Devonian; however, their age of formation is Cretaceous or later. Some of 

the deposits are the result of katamorphic alteration, and some are the result of 

weathered material being transported and deposited in sinkaoles or caverns. The 

presence of alunite in one deposit suggests the possibility that the clay may be the 

result of both katamorphic and hydrothermal alteration.

INTRODUCTION

White clay in Pennsylvania was first mined in about 1890 for use 

in the paper industry as a paper filler and paper coater. The State 

continued to be a leader in production of white clay until 1930. 

However, with the introduction into the market of better quality 

clays from the Southeastern States, white clay in Pennsylvania lost 

its importance in the paper industry.

White clays are being mined or have been mined from near 

Mount Holly Springs in Cumberland County; near Kunkletown in 

Monroe County; several deposits in Centre, Huntingdon, and Blair 

Counties; near Dillsburg in York County; and Narvon in Lancaster 

County (fig. 1). The clays are currently used in making white portland cement, refractory products, and as a carrier for insecticides 

and fungicides. They have also been used for face brick in the past.

Dl
D2 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

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WHITE CLAYS OF PENNSYLVANIA D3

Most of the clays are light gray (N8) to white (N9), but some are 

stained yellow, pink, or brown by iron oxides. Kaolinite is the predominant clay mineral, but illite is as abundant as kaolinite in the 

deposits at Kunkletown, Narvon, and Dillsburg. The quartz or chert 

content averages 30 percent in the Mount Holly Springs deposit, 

about 45 percent in the Kunkletown and Stormstown deposits, and 50 

percent or more in the other deposits; however, within each deposit, 

the amounts differ considerably.

The white clays were considered by previous workers (Stose, 

1907, p. 324; Peck, 1922, p. 3; and Leighton, 1934, p. 1) to be residual 

deposits derived by weathering of feldspathic sandstone, argillaceous 

and cherty limestones, and phyllites. The present investigation has 

found that deposits near Kunkletown, Narvon, and Alexandria are 

residual (derived by chemical weathering in place), which is also 

known as katamorphic alteration. The deposit near Mount Holly 

Springs is also the result of katamorphic alteration, but the presence 

of alunite indicates the possibility of hydrothermal alteration. The 

clay deposit near Dillsburg probably has the same geologic history as 

the one near Mount Holly Springs. The morphology of the clay 

deposits of Centre, Blair, and Bedford Counties in the Gatesburg 

Formation indicates that they are composed of weathered debris 

deposited in caves or sinkholes.

The purpose of this investigation was to study the geology and 

mineralogical and chemical composition of the white clay deposits in 

Pennsylvania. Knowledge of the deposits will contribute to a better 

understanding of white clay resources and may be helpful in determining potential uses for the clay. In addition, knowledge about the 

origin of the clay deposits and a study of the parent material will help 

determine whether the abandoned clay pits can be used for waste 

disposal.

METHODS OF INVESTIGATION

A review was made of the published geologic literature. The 

areal geology of the clay deposit discussed is based on the work of 

several geologists. Stose (1953) and Freedman (1967) mapped the 

vicinity of Mount Holly Springs; Epstein and Epstein (1967) mapped 

the area around Kunkletown, and the geologic map of Pennsylvania 

(Gray and others, 1960) was the primary source of geologic information for all other clay deposits.

Auger-drilling equipment was used to sample the clay deposits. 

This equipment consisted of a power auger mounted on the back of a 

2-ton truck. The drilling method consisted of sampling a 1.5-m interval at a time and pulling the auger from the hole after each interval. 

This was repeated until the desired depth of sampling was reached.
D4 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

When the auger was pulled from the hole after each interval, a 

sample was taken from between the whorls of the leading auger 

flights. A 1.5-m interval usually filled almost two auger flights with 

material. The sample was disturbed, but contamination from the 

walls of the hole was easily cut away from the outside.

The mineralogical and chemical composition of the samples was 

determined in the laboratory by means of X-ray diffraction and 

X-ray fluorescence methods described in an earlier report (Hosterman, 1969a, p. 6 and 7). The whole rock samples were ground to 

minus 170 mesh. The powder was pressed into a pellet 28 mm in 

diameter in an evacuated hydraulic press for a minimum of 30 

seconds at a pressure of 30,000 pounds per square inch (psi). A 50-50 

mixture of boric acid and methyl cellulose was pressed beneath the 

sample in the mold for support. The clay fraction was obtained by 

placing a portion of the sample in water and allowing it to settle for 2 

hours and 3 minutes. The suspended material in the upper 10 centimeters was carefully siphoned off; this material contained the clay 

fraction of less than 4 micrometers (//m) in diameter. An oriented 

aggregate was obtained by sedimenting the clay fraction onto a 

porous ceramic tile and removing the water by vacuum. The ratios of 

clay, silt, and sand were calculated on the basis of dry-weight percentages. Sand was removed by means of a No. 230 sieve, and then clay 

was removed from silt by repeated washings. The description of all 

the samples, in this report, is based on the system of sediment 

nomenclature in Hosterman (1969a, fig. 2).

The X-ray diffraction method for mineralogical identification 

and X-ray fluorescence method for chemical composition are routine. The X-ray diffraction method consisted of using CuKai radiation (1.54050 A) with a diffraction beam monochromator. Most clay 

samples were treated in several ways and examined by X-ray diffraction after each treatment so that various clay minerals could be 

detected. Samples were treated with ethylene glycol to identify 

expandable clay (smectite) and were heated to 300°C to identify 

collapsible clay (mixed-layer clay or vermiculite). Several samples 

were treated with 3N hydrochloric acid to check for the presence of 

chlorite and kaolinite. The clay mineral ratios are based on peakarea ratios obtained from the X-ray diffraction traces. On the basis of 

reproducibility tests, this procedure provides a method for determining the amount of each mineral present to an accuracy of about 

±10 percent. The limestone samples were dissolved by heating samples in a 20-percent solution of acetic acid to concentrate the insoluble material and make identification easier. The X-ray fluorescence 

method consisted of using a Cr-target tube for primary radiation 

with a lithium fluoride analyzing crystal (2c?=4.0267 A) for iron and
WHITE CLAYS OF PENNSYLVANIA D5

titanium and with a pentaerythritol analyzing crystal (2d=8.78 A) 

for calcium, potassium, silicon, and aluminum. All elements are 

reported as oxides, and total iron is reported as Fe2O3. This method is 

not as accurate as the wet-chemical method, but it is found to be 

accurate within 10 percent of the amount of oxide present.

Representative samples from six clay deposits were tested for 

their potential value as paper clays by the Georgia Kaolin Co. The 

brightness, measured as a percentage, was determined by means of a 

reflection meter or brightness tester. The minimum requirement of 

a paper-grade clay is a brightness of at least 80 percent for use as a 

paper filler and at least 85 percent for use as a paper coater. The 

viscosity, in centipoises, is measured with a viscometer in which a 

Brookfield No. 3 spindle is used. The viscosity should be less than 500 

centipoises, but occasionally a viscosity of between 500 and 700 centipoises is acceptable as a paper filler (H. H. Murray, oral commun., 

April 1970).

ACKNOWLEDGMENTS

C. Robert Todd, president, Philadelphia Clay Co.; George F. 

Smith, geologist, Universal Atlas, Division of United States Steel 

Corp.; P. C. Mitchel, former vice president, Harbison-Walker Refractories Co.; and John M. Stevens, president, Woodbury Clay Co., 

granted access to the clay pits, gave permission to auger on the 

property owned or leased by their respective companies, and allowed 

use of geologic data helpful in completing this report. The author 

thanks H. H. Murray, former executive vice president of the Georgia 

Kaolin Co., who kindly granted permission to publish the results of 

six clay samples tested for paper-grade characteristics.

CLAY DEPOSITS NEAR KUNKLETOWN AND SAYLORSBURG, 

MONROE COUNTY

LOCATION AND HISTORY

White silty clay deposits occur between Kunkletown and Saylorsburg, Monroe County, Pa. (fig. 1). The clay deposits currently 

mined are about 1.6 km southeast of Kunkletown. The first clay 

mining near Kunkletown began before 1900 when clay from the 

north side of Chestnut Ridge was used in making soap. Later, white 

brick was made at Kunkletown by the New York and Pennsylvania 

Brick and Tile Co. and, still later, by the Chestnut Ridge White Clay 

Co. In 1932, the Atlas Portland Cement Co. and its successor, the 

Universal Atlas Cement Co., moved its operation to near Kunkletown 

from the north slope of Cherry Ridge, where clay had been mined
D6 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

since 1909. The clay pits currently provide 200 tons of raw material 

per day (Epstein and Hosterman, 1969, p. D94). The clay is trucked 

22 miles to Northampton where it is ground, made into a slurry, and 

blended into a kiln feed used in making white portland cement.

White clay near Saylorsburg was first mined in 1891 when 

Oscar Drehr built a plant to make enameled brick. In 1894, the 

Blanchard brothers of Newark, N.J., took over the plant and made 

dry pressed brick. Fourteen years later in 1908, the Keystone Clay 

and Reduction Co. began operating a plant to produce washed white 

clay (Peck, 1922, p. 2). By 1919, this company was producing about 30 

tons of washed clay per day (Leighton, 1941, p. 185). The white clay 

was used chiefly as a paper filler, and a minor amount was used in the 

manufacture of rubber and paint. In 1917, the Mt. Eaton Clay Co., 

which later became the Pennsylvania White Clay Mining Co., began 

operating a pilot plant and mine 2.4 km southeast of Saylorsburg on 

the north slope of Chestnut Ridge. During the 1920's, this plant 

produced 50 tons of clay per day. The clay was dried, ground, and 

sold as a refractory material for use in foundries and blast furnaces 

(Leighton, 1941, p. 186). The last company to produce clay at Saylorsburg was the Blue Ridge Clay Co.; however, no clay mining has 

been active in this area since the mid-1930's.

GEOLOGY

The clay deposits are the weathered material of a heterogeneous 

assemblage of Upper Silurian through Middle Devonian limestones, 

shales, siltstones, sandstones, and dolomites. Unweathered outcrops 

of these rocks, west of Bossardsville, Pa., are rare, whereas fresh 

rocks crop out in abundance northeast of Bossardsville and have 

been described by Epstein and Epstein (1967). The weathered part of 

the rocks or saprolite is probably more than 30.5 m thick in many 

places, and a hole drilled by the cement company penetrated 55.5 m 

of clay without striking fresh rock (G. F. Smith, oral commun., 1969).

Clay has been and is currently being mined from weathered 

parts of the New Scotland Formation, Shriver Chert of the Oriskany 

Group, and Buttermilk Falls Limestone. Where fresh, these rocks 

are generally cherty, silty, argillaceous limestones and limy shales. 

They have been weathered to silty clays and clayey silts. The best 

quality clays are white to yellowish gray, but some are stained various shades of pink and orange. In some of the deposits, the chert has 

not been completely leached and remains as hard nodules. The formations that weather to clay become thinner and less pure (less 

calcareous and more siliceous and iron stained) westward, and the 

clay west of Little Gap is too low grade and has never been mined.
WHITE CLAYS OF PENNSYLVANIA D7

The thickest deposits occur in the Saylorsburg area where they have 

been extensively worked (Peck, 1922). No clay deposits have been 

found east of Bossardsville and the Wisconsin terminal moraine. 

Thus, the most promising areas for the prospecting are about 3.2 km 

east of the presently active area where pit operations should prove 

most profitable, and between Kunkletown and about 1.6 km west of 

Saylorsburg, where underground workings might be considered.

The clay-bearing units crop out in long narrow belts and are 

repeated by folding (fig. 2). Two of the pits are confined to near the 

top of the ridge where overburden is not a great problem. The third 

pit along the side of the ridge has an overburden of Palmerton 

Sandstone, which is mined for sand. Underground mining has not 

been attempted recently as it once was near Saylorsburg (Peck, 1922).

COMPOSITION

The mineralogy of fresh bedrock samples and equivalent weathered rock samples was studied to determine the changes that took 

place as a result of katamorphic alteration. The unweathered rocks, 

on which the clays are developed, are chiefly argillaceous limestones 

and limy shales. Carbonate minerals and quartz make up most of 

these rocks, and chlorite and 2M illite are the dominant clay minerals. Illite was found to be only a minor constituent in samples of fresh 

Buttermilk Falls Limestone, but it is abundant in the rocks weathered from the limestone. Kaolinite, which is very abundant in the 

weathered rocks, was not identified in the fresh, unweathered rocks. 

Quartz or chert is the only other mineral present with illite and 

kaolinite in all the weathered material; chlorite, calcite, and dolomite 

have been replaced owing to katamorphic alteration. The overall 

chemical average of the weathered rocks (table 1), as determined by 

X-ray fluorescence methods, is similar to the average raw material 

used by the Universal Atlas Cement Co. from the pits near Kunkletown: 80.8 percent SiO2 , 12.1 percent A12O3 , 0.6 percent Fe2O3 , 0.6 

percent CaO, and 0.3 percent MgO (G. F. Smith, oral commun., 

September 1967).

Clay tests published by Ries and others (1922, p. 115) show that 

clay from near Kunkletown has an approximate drying shrinkage of 3 

percent, a fired linear shrinkage of 3 to 12 percent, and absorption of 

about 10 percent. The fact that no statement was made about the 

workability indicates that it is probably poor. The paper-grade tests 

of a representative composite sample showed a brightness of 57.6 

percent. The viscosity, tested on samples containing 71 percent 

solids, is 160 and 255 centipoises at 10 and 100 revolutions per 

minute, respectively.
D8 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS
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New Scotland Formation saprolite: 

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Do.... ............................................ .

Silty clay (5Y9/D......... .....................

Stormville Member of Coeymans 

Formation: 

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Clayey silt (7.5Y9/1) ........................

Clayey silt (7.5Y9/2) ......................

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Do.......... .. .............................

Silty clay (7.5Y9/1). .........................

Do. .......... .................................

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Silty clay (N9). ................................

Siltv clay (7.5Y9/1 )..........................

Do.............. .................................

Silty clay (10YR7/3) . ......................

Siltv clay (7.5Y9/1) .. ........................

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WHITE CLAYS OF PENNSYLVANIA D13

NARVON CLAY PIT, LANCASTER COUNTY

The clay pit near Narvon, in eastern Lancaster County, 6.4 km 

west of Honeybrook, lies along the north slope of Welsh Mountain. 

Welsh Mountain is underlain by the resistant Chickies Quartzite of 

Late Proterozoic age. The upper part of the Chickies is composed of 

thin-bedded siltstone and argillite that weathers to a yellowish-gray 

and light-gray clayey silt. The deposit was first discovered in 1875 by 

a railroad crew and has been mined almost continuously from two 

pits since 1880. The property is presently owned by the Narvon 

Mines, Ltd. The clayey silt produced was dried, ground, and bagged 

and sold for use in filler materials, ceramics, insecticide carriers, 

and water purification.

Seven samples were taken vertically at 1.5-m intervals from the 

west face of the pit; the first sample was taken 3 m below the soil 

overburden. The clayey silt is composed of approximately 8 percent 

sand, 62 percent silt, and 30 percent clay (table 2). Quartz is the 

predominant mineral in the sand and silt fractions, and the clay 

fraction is composed of kaolinite and illite in a 7:3 ratio. A papergrade test of a composite sample from the pit showed a brightness of 

73 percent. The viscosity, tested on samples containing 71 percent 

solids, is 1,500 and 913 centipoises at spindle speeds of 10 and 100 

revolutions per minute, respectively. The silty clay is not a papergrade material and, according to Leighton (1934, p. 15), does not 

have the properties of china clay.

CLAY PIT NEAR DILLSBURG, YORK COUNTY

The clay pit 3.4 km west of Dillsburg (fig. 1) is in an eastern 

extension of the same geologic setting as the clay pits near Mount 

Holly Springs. According to Leighton (1934, p. 14) and Stose (1953), 

the deposit is residual clay derived from the Harpers Schist. However, it is probably a residual weathered phyllite of the Tomstown 

Formation. The Tomstown is composed of thick-bedded, dense, 

bluish-gray dolomite, light-gray thin-bedded limestone, and lightgray phyllite. The thickness of the formation is difficult to calculate 

because exposures are very rare. Freedman (1967, p. 37) estimated 

its thickness to be about 300 m. The Tomstown is the youngest unit in 

the immediate area. It is underlain, from youngest to oldest, by the 

Antietam Quartzite, the Montalto Quartzite Member of the Harpers 

Schist, and the Weverton Quartzite. These formations are Late 

Proterozoic to Early Cambrian in age (Stose, 1953).

On the basis of 11 samples (table 3) collected from the surface of 

the pit and from a 15-m auger hole, the material has an average 

grain-size composition of clayey silt. The color ranges from a pale
D14 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

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WHITE CLAYS OF PENNSYLVANIA D15

yellow to a weak yellowish orange owing to an iron oxide content that 

ranges from 1 to 24 percent (table 3). Kaolinite and illite occur in a 

ratio of approximately 7:3. Quartz makes up the silt and sand fractions, and goethite is abundant enough in some samples to make it 

almost an iron ore. The deposit has very little value economically, 

except possibly in making red building or face brick. It is presently 

owned by the Boy Scouts of America, York-Adams Area Council, 

who operate a summer camp nearby.

CLAY DEPOSITS NEAR MOUNT HOLLY SPRINGS, 

CUMBERLAND COUNTY

LOCATION AND HISTORY

As many as five white clay deposits in the vicinity of Mount Holly 

Springs have been worked during the past 75 years. The only one 

being worked and available for sampling at present is the open pit at 

Toland owned by the Philadelphia Clay Co.

All the abandoned clay deposits and the deposit at Toland are 

south and southwest of Mount Holly Springs in a narrow valley 

enclosed by two parallel southwest-trending ridges. The two ridges, 

Piney Mountain and South Mountain, are the northern extension of 

the Blue Ridge Mountains, which extends from Pennsylvania to 

Georgia.

White clay deposits in the South Mountain area have been mined 

intermittently since about 1890, but no accurate production data are 

available. The clay was probably first recognized in the mid-1800's 

by prospectors looking for iron ore. Between 1890 and 1910, at least 

five companies mined clay in the area. Four of these companies had 

facilities for beneficiating the clay that was sold for use as a paper 

filler. One company in Mount Holly Springs used the raw clay for 

making cream to light-buff brick (Stose, 1907, p. 330). By 1930, 

however, only two companies were mining clay: the Philadelphia 

Clay Co. had a 100-ton daily capacity mill for washing and drying 

clay, and the Medusa Portland Cement Co. was mining and shipping 

raw clay for use as a whitener in portland cement (Leighton, 1934, p. 

13). By the mid-1960's, the Philadelphia Clay Co. was the only producer of clay. This company, using earth-moving equipment, has 

changed from underground to open-pit mining and is currently 

producing about 40,000 tons of raw clay a year for use as a whitener 

in portland cement.

GEOLOGY

The white clay deposits in the vicinity of Mount Holly Springs 

occur in phyllite beds of the Tomstown Formation. This formation is
D16 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

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WHITE CLAYS OF PENNSYLVANIA D17

composed of thick-bedded, dense, bluish-gray dolomite, light-gray 

thin-bedded limestone, and light-gray phyllite. The dolomite weathers to a tough reddish-brown residuum composed of kaolinite and 

illite; the limestone weathers to a sticky yellow clay consisting of 

illite and kaolinite; and the phyllite weathers to a variegated silty 

clay containing predominantly kaolinite and some illite.

The Mount Holly Springs area has been intensely folded and 

faulted. According to Stose (1953), South Mountain is an anticline 

composed of the Montalto Quartzite Member of the Harpers Schist in 

the core and Antietam Quartzite on the flanks; Piney Mountain is 

homoclinal and is composed of the Weverton Quartzite, Montalto 

Quartzite Member, and the Antietam Quartzite; the longitudinal 

valley of Mountain Creek is synclinal and underlain by the Tomstown 

Formation. Freedman (1967) made two major changes in Stose's geologic map in the area of the clay deposits. He believed that the quartzite underlying South Mountain is the Montalto Quartzite Member 

instead of Antietam Quartzite and that a major fault is along the 

southeast-facing slope of South Mountain. The author agrees with 

Freedman's interpretation on the basis of the exposure made available by open-pit mining and the data obtained from two auger holes. 

The fault is steeply dipping to the southeast and has a relative 

upward movement on the northwest side. The phyllite beds of the 

Tomstown exposed in the Toland pit are tightly folded and contorted. 

All the clay deposits in the Mount Holly Springs area and the 

clay deposit near Dillsburg undoubtedly were formed in the same 

geologic environment. All deposits are in the phyllite beds of the 

Tomstown and are located near the fault contact with the Montalto 

Quartzite Member. This fault is probably the principal reason for 

the formation of these deposits.

The white clay deposit at Toland is lens shaped, measuring 

approximately 60 m at its maximum width and 500 m in length (fig. 

3); its vertical extent is probably about 90 m. The northern boundary 

of the deposit, where it is in fault contact with the quartzite of the 

Montalto Member, is sharp and straight. The southern boundary is 

gradational; the white clay grades into yellow, pink, red, and brown 

silty clay. This varicolored silty clay, which is about 60 m wide, 

grades into grayish-green to light-gray phyllite and calcite-veined 

limy phyllite of the Tomstown Formation.

Two auger holes were drilled in the floor of the pit (fig. 3). Auger 

hole 2 penetrated white clay for its entire depth of 46 m. Auger hole 1 

penetrated white clay to a depth of 24 m, and then variegated silty 

clay (table 4). The projection of the variegated silty clay-white clay 

contact at the surface with its position at a depth of 24 m in auger hole 

1 indicates an approximate dip of 60° N. If dip of this contact does not
D18 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS
WHITE CLAYS OF PENNSYLVANIA D19

change at increased depth, the deposit wedges out against the steeply 

dipping fault at about 90 m below the present level of the pit floor. 

Bedding in the white clay is not distinguishable because open-pit 

mining has exposed only clay that has been disturbed by previous 

underground mining. Adjacent to the white clay, the sandy beds in 

the variegated silty clay, although very contorted, have an average 

dip of 60° N. The similarity between the dip of the beds and the dip of 

the contact near the haulageway indicates that there may be some 

beddingicontrol to the alteration (p. D34), even though the contact 

does cross the bedding toward the east and west ends of the pit.

COMPOSITION

The white clay, the varicolored silty clay, and the weathered 

phyllite in the Philadelphia Clay Co. pit at Toland show progressive 

differences in particle-size content, clay-mineral ratio, and SiOi and 

FeiOs content (table 5). As depth increases, the white clay decreases 

in sand and silt and increases slightly in clay. The sand and silt in the 

white clay are composed chiefly of quartz and trace amounts of 

muscovite. The sand and silt in the variegated color silty clay are 

composed of fine-grained quartz and some hematite and limonite. 

The sand and silt in the slightly weathered phyllite are composed of 

fine-grained quartz and small amounts of muscovite, biotite, and 

magnetite. Some of the phyllite contains limy beds and calcite veins.

The SiOi content of the rocks at the surface decreases from the 

white clay through the variegated silty clay to the weathered phyllite, whereas both the FeiOs and KiO contents increase. The Al2Os 

content varies only a few percent without any discernible trend 

except for a slight decrease from the variegated silty clay into the 

weathered phyllite. The TiOi content remains constant (Hosterman, 

1969b, fig. 3). In addition to these chemical variations, the following 

mineralogical changes take place: kaolinite is most abundant in the 

white clay and least abundant in the phyllite; illite is least abundant 

in the white clay and most abundant in the phyllite. The differences 

in chemical and mineralogical composition may be due to weathering, but they may also be due to differences in the lithology. The A12C>3 

content does not change very much as a result of either weathering or 

clay mineralogy. An explanation for this is that the AliOs content in

4 FIGURE 3. Clay pit of the Philadelphia Clay Co. at Toland showing location of auger 

holes. A. View looking west shows Montalto Quartzite Member of the Harpers 

Schist on right (north), white clay in center, and varicolored silty clay on left (south). 

B. View looking east shows Montalto Quartzite Member on left (north) being 

stripped, white clay in center, and varicolored clay on right (south). (Heavy line 

indicates fault contact; U,up; D.down.)
D20 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

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WHITE CLAYS OF PENNSYLVANIA D21

illites can be almost as high as it is in kaolinite. This is confirmed by 

the chemical analyses of some illites published by Grim (1953, p. 372).

TABLE 5. Average composition of clay and enclosed rocks at the Toland pit

Clay minerals

No. of Sand Silt Clay Kaolinite Illite Smectite SiO2 A12O3 Fe2O, 

samples (percent) (ratio) (percent)

White clay ..............................

Variegated silty clay............

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The nature and attitude of the southern boundary of the white 

clay deposit are obtained from observations in the clay pit and from 

the chemical and mineralogical data from auger hole 1. The auger 

hole (table 4) was drilled approximately 18 m from the contact with 

the variegated silty clay. The high SiO2 and low A12O3 content of the 

first sample (table 4) is due to contamination from the quartzite and 

sand washed into the clay pit from the nearby spoil bank. The samples taken at 3 and 6 m are slightly higher in silt content that the 

average white clay at increased depth; therefore, the SiO2 content is 

higher and the A12O3 content is lower than the average-grade white 

clay. At a depth of 24 m, the hole penetrated variegated silty clay. At 

a depth of 24 m, the hole penetrated variegated silty clay. The boundary between the two clays is placed at a marked color change from 

white (N9) and yellowish white (10YR9/1) to light orange pink 

(5YR8/2 and 10YR7/2) (Munsell Color Co., 1954). At this boundary, 

the Fe2O3 content increases from 0.5 percent (yellowish white) to 1.2 

percent (light orange pink). However, the fact that the SiO2 content 

remains fairly constant indicates no increase in the amount of sand 

and silt present. In addition, illite increases and kaolinite decreases. 

The kaolinite-illite ratio above 18 m is 9:1 and below 18 m is 8:2 (table 

4). Traces of alunite were observed in X-ray diffraction patterns in 

samples from between 9 and 24 m (Hosterman, 1969b, fig. 6).

The chemical and mineralogical data obtained from samples of 

auger hole 2 indicate that weathering or katamorphic alteration may 

have been the main geologic process, but evidence for hydrothermal 

alteration is also present. Auger hole 2 was drilled in white clay 

approximately 44 m from the contact with variegated silty clay. The 

high SiO2 and low A12O3 content (table 4) of the surface samples is 

possibly due to quartz contamination resulting from blasting and 

stripping of the Montalto Quartzite Member of the Harpers Schist on 

the mountain slope above the clay pit. From 6 to 45.5 m, the SiO2 

decreases from 73 to 63 percent, the A12O3 increases from 18 to 25
D22 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

percent, the Fe2 Os and TiO2 are relatively constant, and the K2O is 

fairly constant down to 39.5 m but increases from 1.1 to 2.4 percent 

below 39.5 m. The kaolinite-illite ratio is greater than 9:1, and the 

color, with one exception, is white (N9) in all 16 samples examined. 

Alunite occurs in trace amounts from 12 to 39.5 m and in slightly 

more than trace amounts from 39.5 to 45.5 m. The bulk lithology of 

the white clay is virtually the same from 6 to 45.5 m with very little 

variation in the sand-silt-clay ratios (table 4). Thus, the steady 

increase of A12O3 as depth increases and the complementary decrease 

of SiO2 cannot be attributed to differences in lithology. This increase 

in A12O3 content as depth increases, however, is the reverse of the 

change normally observed in a weathering profile (Hosterman and 

others, 1960, p. 13), but indicates hydrothermal alteration.

Tests by Shaw (Leighton, 1934, p. 12) indicated that the clay 

from the Mount Holly Springs area has good plasticity, low green 

strength, and fires to a light-cream to light-gray color. Paper-grade 

tests of a representative sample from the Philadelphia Clay Co. pit 

indicated a brightness of 79.3 percent; viscosity, tested on samples 

containing 68 percent solids, is 700 and 656 centipoises at spindle 

speeds of 10 and 100 revolutions per minute, respectively. White clay 

from this deposit tested the highest in paper-grade quality of all 

white clays in Pennsylvania.

CLAY DEPOSITS IN THE GATESBURG FORMATION OF 

CENTRE, BLAIR, HUNTINGDON, AND BEDFORD COUNTIES

LOCATION AND HISTORY

All the clay deposits discussed in this section are in the Gatesburg Formation of Late Cambrian age. The three largest and most 

recently mined clay pits in the Gatesburg are in Stormstown, Centre 

County, operated by the Harbison-Walker Refractories Co.; Oreminea 1, Blair County, owned by the Woodbury Clay Co.; and Oreminea 

2, Blair County, operated by Grannas Brothers, Inc. Other older and 

much smaller clay pits in the Gatesburg are in Baileyville and Kelsey, Centre County; Dungarvin, Pennington, and Shoenberger, Huntingdon County; Martinsburg, Blair County; and Ore Hill and Bakers Summit, Bedford County (fig. 4).

The historical records on production of clay from the Gatesburg 

Formation in central Pennsylvania are very sketchy. White clay was
WHITE CLAYS OF PENNSYLVANIA D23

probably first found in the middle to late 19th century when there 

was considerable prospecting for iron ore. During World War I, the 

amount of imported white clay from Europe was greatly reduced. 

This stimulated the mining of white clay in this area (Moore, 1922) 

that lasted until about 1935. World War II caused a renewal in the 

production of white clay for the refractory industry, which then 

remained fairly steady for about 20 years. Since 1963, the amount of 

clay produced by the industry from central Pennsylvania has 

decreased steadily; at present only a very small amount is mined 

each year.

78«30' 78«00'

40°45' 

40°30 

40°15' 

EXPLANATION

Gatesburg 

Formation

Clay pit names

1. Stormstown

2. Baileyville

3. Kelsey

4. Dungarvin

5. Pennington

6. Shoenberger

7. Oreminea

8. Williamsburg

9. Martinsburg

10. Ore Hill

11. Bakers Summit

12. Alexandria

13. Petersburg

14. Shirleysburg

FIGURE 4. 'Outcrop belt of the Gatesburg Formation (shaded areas) containing 

clay deposits and clay pits (X) in the Oriskany Group in Centre, Blair, Hunting 

don, and Bedford Counties, Pa., modified from Gray and others (1960).
D24 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

GEOLOGY

The clay deposits in the Gatesburg Formation are within a more 

or less homogeneous assemblage of Upper Cambrian silty dolomites. 

According to Butts and others (1939, p. 10), the Gatesburg is about 

533 m thick and is composed predominantly of thick-bedded, coarsely 

crystalline, medium-gray dolomite with a small amount of thinbedded, fine-grained medium-gray dolomite and a few beds of sandstone generally cemented with dolomite or calcite. The best exposure 

of unweathered Gatesburg is southeast of Tyrone on the BlairHuntingdon County line (fig. 4) where Pennsylvania Highway 350 

cuts through the dolomite along the Little Juniata River 0.8 km 

southeast of Birmingham. Six samples of rock were taken at random 

from exposures in a roadcut that is 370 m long. One sample contains a 

small amount of calcite in the dolomite, and the others are all dolomite. The acid-insoluble residue from these rock samples averages 

approximately 25 percent of the whole rock and ranges from 9 to 40 

percent. The grain size of the insoluble material is predominantly 

clay and silt with a trace of sand; however, half of the insoluble 

material from one sample is sand. The insoluble material is composed 

of illite, some chlorite, quartz mainly in the form of chert, feldspar 

(chiefly microcline), and magnetite.

All clay deposits in the Gatesburg Formation are undoubtedly 

products of similar geologic environments. The outcrop pattern of 

the Gatesburg (fig. 4) shows a series of fault contacts on the north and 

northwest sides of the belt, and several additional faults are known to 

cut the formation. Because exposures are scarce and poor, many 

more faults and fractures than are indicated on the map may exist in 

these rocks. The lack of bedding or sedimentary features is evident in 

the recently worked clay pits, such as Oreminea 1, Oreminea 2, and 

Stormstown. Faults and fractures, along with the lack of bedding, 

may be a major factor in the formation of the clay deposits.

The clay body in Oreminea 1, the largest of the elliptical types, is 

300 m long, 150 m wide, and about 30 m deep. Stormstown (fig. 5), the 

largest of the lens types, is 75 m wide, more than 600 m long, and 6 m 

deep. This deposit is probably several hundred meters longer but is 

narrower to the west where the clay has not been removed. The 

deposit at Oreminea 2 is elliptical in shape measuring 90 by 200 m 

and 9 m deep. The size of the other clay deposits that could be 

measured are Baileyville, 90 by 200 m; Kelsey, 20 by 100 m; Dungarvin, 200 by 400 m; Shoenberger, 60 by 300 m; Martinsburg, 60 by 150 

m; and Bakers Summit, about 60 by 60 m.
WHITE CLAYS OF PENNSYLVANIA D25 

COMPOSITION

At the Stormstown clay pit (fig. 5), 11 samples were taken from a 

19-m auger hole and 23 samples were taken at 3-m intervals across 

the 75-m exposed face of the clay pit (table 6). The grain-size composition of the 34 samples which averaged 34 percent sand, 10 percent 

silt, and 56 percent clay, indicated that the deposit is a very sandy 

clay. The sand and silt fractions are composed of quartz, and the 

clay-size fraction is virtually pure kaolinite. No evidence of any 

mineralogical or chemical changes was found at greater depths 

(table 6); such changes might be expected if the deposit is the result of 

katamorphic alteration in situ. The only noticeable variation is from 

the samples taken across the face of the pit. Here, there is a very 

slight increase in the amount of iron at the north and south edges of 

the pit. The color of the clayey sand is predominantly white to yellowish white, and where the iron content increases (table 6), it is slightly 

pink or orange.

Physical tests published by Ries and others (1922, p. 95) stated 

that the clay at Stormstown (Blair property) has an absorption of 

15.7 percent, hardness of steel, and a faint cream-white color when 

fired at 1,350°C. They also indicated that the clay would be suitable, 

after washing, for whiteware and pottery. The paper-grade tests of 

the Harbison-Walker Refractory Co. clay pit near Stormstown show 

a brightness of 72.8 percent. The viscosity, tested on samples containing 71 percent solids, is 270 and 130 centipoises at spindle speeds of 

10 and 100 revolutions per minute, respectively. These tests indicate 

that the clay is not of paper-grade quality.

The clay in the Oreminea 1 pit has been mined out, and it was not 

possible to obtain a representative sample of the material produced 

in this area. However, samples of similar, though possibly of somewhat lower grade, clay were taken when five auger holes were 

drilled in the vicinity of the pit (fig. 6 and table 7). The average 

grain-size composition of the 38 samples from these five holes, which 

was 40 percent sand, 33 percent silt, and 27 percent clay, indicated 

that this material is a clayey silty sand. The sand and silt fractions 

are composed of quartz, and the clay-size fraction is mostly kaolinite 

and small amounts of illite. No evidence of mineralogical or chemical 

changes was found at greater depths (table 7); such changes might be 

expected if the deposit is a result of weathering in place. The papergrade tests of representative samples from the five auger holes near 

the Oreminea 1 clay pit show a brightness of 72.7 percent. The 

viscosity, tested on samples containing 71 percent solids, is 80 and 85 

centipoises spindle speeds of 70 and 100 revolutions per minute, 

respectively.
D26 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

*2(T«2i

FIGURE 5. Clay mine in the Stormstown pit, Centre County. The view is looking east 

and shows the north and south limits of the pit and the location of the auger hole. 

Numbers refer to sample locations.

At the Oreminea 2 clay pit, one auger hole was drilled to a depth 

of 9.5 m, and 10 samples were taken (table 7 and fig. 6). The average 

grain-size composition of this material, which is 17 percent sand, 35 

percent silt, and 48 percent clay, indicates that it is a silty clay. The 

sand and silt fractions are composed of quartz, and the clay fraction 

is chiefly kaolinite and small amounts of illite. The paper-grade tests 

of representative samples from the Oreminea 2 clay pit showed a 

brightness of 75.8 percent. The viscosity, tested on samples containing 71 percent solids, is 2,710 and >1,000 centipoises with spindle 

speeds of 10 and 100 revolutions per minute, respectively.

Samples taken from five of the smaller older clay pits in the 

Gatesburg Formation were analyzed for mineralogical composition 

(table 8). In all samples, the sand and silt fractions are composed of
WHITE CLAYS OF PENNSYLVANIA D27

quartz. The clay fraction of a yellowish-gray, clayey sandy silt sample from the Baileyville pit contains kaolinite, illite, and smectite in 

approximately equal amounts. The high content of illite and smectite 

makes material from this pit undesirable for refractory products. 

The Dungarvin clay pit contains almost white, clayey silt that is 

composed of quartz and kaolinite and small amounts of illite. A 

sample from the Pennington pit proved to be a true clay, containing 

more than 80 percent clay-sized material. The clay is very pale 

orange and is composed of kaolinite and a trace of illite. The exposed 

material at the Shoenberger pit is yellowish-gray, silty clay composed chiefly of kaolinite and some illite. The pit near Martinsburg 

contains almost white, silty clay of which the clay fraction is 90 

percent kaolinite and 10 percent illite.

CLAY DEPOSITS IN THE ORISKANY GROUP 

OF HUNTINGDON COUNTY

In Huntingdon County, central Pennsylvania, the upper part of 

the Oriskany Group of Early Devonian age weathers to a white silty 

clay. The Oriskany Group can be divided into an upper unit of 

thick-bedded, coarse-grained sandstone (Ridgeley Sandstone) and a 

lower unit of chert and shale (Shriver Chert). Both units are typically 

cemented by calcite. The clay deposits are found in residual material 

derived from the lower chert and shale unit.

The refractory properties of these white clays were first recognized in 1870 when clay from the Alexandria pit was used to line 

local iron furnaces. During and after World War I, the white clay 

was used primarily by the steel mills as a mortar in laying refractory 

brick for coke ovens and open-hearth furnaces. Since World War II, 

the white clay has been used with flint clay in making refractory 

brick. In the past, these clay deposits were prospected and tested \$, 

paper and china-clay companies, but records do not indicate that th*e* 

white clay was used either as a filler or in chinaware. The Alexandria Fire Clay Co. mined clay from the Shriver Chert at Alexandria, 

Huntingdon County, until the late 1970's. Other old clay pits in the 

Shriver Chert are found near Petersburg and Shirleysburg, Huntingdon County (fig. 4).

Samples from three of the clay pits were analyzed for their 

mineralogical composition (table 9). A representative sample from 

the Alexandria pit is a white clayey silt composed of quartz, illite, 

and some kaolinite. At the old Shirleysburg pit, the material is a 

light-gray silty clay composed of quartz and equal amounts of kaolinite and illite.
D28 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

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Near Frankstown, Blair County, at the General Refractories Co. 

sand quarry, the Ridgeley Sandstone is overlain by a 3.5 m bed of 

silty clay. This residual clay is probably derived from greenish-gray 

shale of the Onondaga Formation. The pale red silty clay is composed 

of quartz and equal amounts of kaolinite and illite (table 9).

TABLE 8. Mineralogical composition of clay from five small clay pits in the Gatesburg 

Formation, Centre, Huntingdon, and Blair Counties

Grain-size Clay mineralsdistribution , atio) 

Clay pit Description (percent)

Sand Silt Clay Kaolinite Illite Smectite

Baileyville ............ Clayey sandy silt (10YR8/1)2 ...... 27 37 36 4 2

Dungarvin ............ Clayey silt (N9).............................. 17 48 35 9 1

Pennington............ Clay (10YR8/3)................................ 4 15 81 9.5 .5

Shoenberger ........ Silty clay (10YR8/1)...................... 3 46 51 9 1

Martinsburg ........ Silty clay (N9).................................. 5 42 53 9 1

1 Based on X-ray diffraction peak area ratios.

2 Color designations are based on the "Munsell Color Chart" (Munsell Color Co., 1954).

TABLE 9. Mineralogical composition of clay from three small pits in the 

Oriskany Group, Huntingdon County

Grain-size c, minerals, 

distribution (ratio) 

Clay pit Description (percent)

Sand Silt Clay Kaolinite Illite Smectite

Alexandria.............. Clayey silt (N9)2 .................. 11 49 40 2 8

Shirleysburg.......... Silty clay (N7)...................... tr 35 65 5 5

Frankstown............ Silty clay (5R5/2)................ 14 42 44 5 5

1 Based on X-ray diffraction peak area ratios.

2 Color designations are based on the "Munsell Color Chart" (Munsell Color Co., 1954).

ORIGIN OF THE WHITE CLAY DEPOSITS

The white clay deposits in Pennsylvania were formed by one or 

more geologic processes. Some of the clay deposits have been formed 

by katamorphic alteration, at least one clay deposit has been, in part, 

hydrothermally altered, and several clay deposits accumulated by 

sedimentary processes.

The deposits near Kunkletown and Saylorsburg, Monroe County, 

were formed by katamorphic alteration. The geological, mineralogical, and chemical data indicate that the clay deposits were derived 

from cherty, limy shales and argillaceous limestones. This alteration 

is the result of leaching by downward-percolating meteoric water in 

the New Scotland Formation, Shriver Chert, and Buttermilk Falls
WHITE CLAYS OF PENNSYLVANIA D33

Limestone. The following changes were observed: (1) calcite and 

dolomite are completely removed by chemical weathering; (2) chlorite, present in the fresh rock, is not found in the weathered rock; (3) 

illite occurs in approximately equal amounts in both the fresh and 

weathered rocks, but its crystalline state changes from 2M polymorph in the fresh rock to Md polymorph in the weathered rock; and 

(4) kaolinte is found only in the weathered rock, and it probably is a

1300

\\vt-.is, :":- " M

A

1500 FEETn

1000 FEET

500 1000 1500 FEET

EXPLANATION

Contact ^iiix 

(approximately located) Clay pit

Gatesburg Formation 

-Ggm, Mines Dolomite Member

Fault O

Iron Ore Pit

 

Auger Hole

FIGURE 6. Location of auger holes near the Oremineal and Oreminea 2 clay pits. 

From Gray and others, 1960.
D34 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

product of chlorite. The volume loss of 40 to 70 percent is a result of 

leaching the carbonates. The little or no difference in the amount of 

quartz or chert found in the fresh and in the weathered rocks indicates some loss in this mineral during leaching and with the volume 

change. The generally well preserved tectonic and sedimentary features in the pit face prove that the white silty clay is a sedimentary 

rock saprolite.

Narvon pit, Lancaster County, contains clayey silt derived from 

thin-bedded siltstone and argillite beds of the upper part of the 

Chickies Quartzite. The well-preserved sedimentary features in the 

pit face indicate that the deposit is also a sedimentary rock saprolite 

resulting from katamorphic alteration.

The clay deposits in the vicinity of Mount Holly Springs, Cumberland County, including the deposit near Dillsburg, York County, 

could have formed by katamorphic alteration, hydrothermal alteration, or both. Stose (1907, p. 323) proposed that the origin of the 

deposit was by weathering. However, the chemical and mineralogical data suggest that these clay deposits were formed, at least in part, 

by hydrothermal alteration (Hosterman, 1969b, p. B72). Although a 

likely source for hydrothermal activity has not been recognized, 

water heated at considerable depth may have moved upward along 

the faults associated with the clay deposits.

The chemical analyses, particularly the AbOs content of samples 

from auger hole 2 (table 4) supports the evidence of hydrothermal 

origin and does not support the theory that the white clay was formed 

exclusively as a residuum resulting from katamorphic alteration. In 

most weathering profiles the katamorphic alteraton shows that SiO2 , 

Fe2O3, and K2O are leached near the surface and increase in amount 

as depth increases and that the A12 O3 has its maximum amount at the 

surface and gradationally decreases toward the parent material. At 

the Philadelphia Clay Co. pit, the white clay could be considered to be 

the most weathered, the variegated silty clay the partially weathered, 

and the phyllite the unweathered parent material. Fe2O3 and K2O 

show a normal katamorphic alteration profile by increasing as depth 

increases, but hydrothermal alteration, at least in part, is indicated 

by SiO2 decreasing and A12O3 increasing as depth increases. The 

total sand and silt content remains constant below 20 feet; therefore, 

the decrease of SiO2 cannot be due to a downward decrease in sandor silt-size quartz. Also, as depth increases, the amount of clay does 

not increase to account for the downward increase in Al2Os (table 4). 

Alunite accounts for part of the A12O3 increase, but it occurs only in 

trace amounts. The additional Al2Os content could be caused by a 

slight increase of aluminum"in the kaolinite lattice and to the presence of allophane, which is amorphous to X-ray detection and almost
WHITE CLAYS OF PENNSYLVANIA D35

impossible to identify by differential thermal analysis in the presence of kaolinite. Kaolinite, the most abundant mineral present, can 

be formed either by hydrothermal alteration or by katamorphic 

alteration.

Semiquantitative spectrographic analyses by Joseph L. Harris, 

U.S. Geological Survey, of 16 samples from auger hole 2, also indicate the possibility of hydrothermal alteration. Three elements 

found associated with hydrothermal activity were found to be higher 

than average for most clays. The lead (Pb) averaged 50 parts per 

million (ppm) in auger hole 2 (table 4), and in most other clay material it is only about 10 ppm. The copper (Cu) content ranged from 20 

to 150 ppm, slightly higher than in most other clays, which rarely 

have more than 50 ppm. The unique element was cerium (Ce), which 

averaged 200 ppm, and it is not detectable in most other clay materials. The chemical and mineralogical evidence indicates that the 

white clay deposits near Mount Holly Springs were probably formed 

by hydrothermal alteration. The surface features, the presence of 

supergene iron ore deposits, and the weathered phyllite all indicate 

that katamorphic alteration occurred after hydrothermal alteration.

The clay deposits found in the Gatesburg Formation of central 

Pennsylvania were formed by katamorphic alteration, erosion, and 

subsequent deposition. The chemical reaction of slightly acidic 

ground water leached the dolomite of the Gatesburg. Faults and 

fractures in the dolomite probably controlled the direction and 

course of the ground water creating caverns and sinkholes. Along 

with the removal of carbonate minerals, much of the insoluble material, which constitutes approximately 25 percent of the fresh rock, 

was chemically altered. The illite, chlorite, and feldspar from the 

parent rock are weathered to kaolinite with the removal of alkalies 

and iron. The iron from magnetite and chlorite was converted to 

soluble iron. Quartz remained unaltered. This chemically weathered 

material was eroded and deposited in previously formed sinkholes 

and caverns. Most of the clay deposits in the Gatesburg occur along 

the flanks of ridges or knolls of more resistant sandy material. The 

presence of a deposit is commonly indicated by a small depression in 

the land surface. The deposits are either elliptical or lens shaped. No 

bedding or sedimentary features have been observed in any of the 

pits. The grain-size distribution, (table 6 and 7) which shows a complete heterogeneity, indicates a lack of sorting. Also, none of the 

chemical or mineralogical data give evidence for katamorphic alteration in place, which suggests that the clay was transported and 

deposited in sinkholes and caverns of the Gatesburg Formation.

The clay deposits found in the Shriver Chert of central Pennsylvania have an origin similar to those deposits near Kunkletown and
D36 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

Saylorsburg. They are products of katamorphic alteration, in place, 

of cherty limy shales. This alteration is the result of leaching by 

downward-percolating slightly acidic ground water.

The white clay deposits near Mount Holly Springs and Dillsburg 

and those in the Gatesburg Formation of central Pennsylvania are 

near iron pits that have been productive in the past. A close relationship exists between the white clay and iron oxide deposits. Surface 

waters that had a high oxygen content penetrated the fresh parent 

rock along fracture or fault planes and along bedding planes. The 

carbonate minerals were removed first by leaching, followed by the 

leaching of iron, potassium, and magnesium from illite, chlorite, and 

the accessory minerals. These elements were carried away in solution, and a residual deposit was left that was composed primarily of 

white kaolinitic silty clay. The iron, derived partly from illite, but 

chiefly from the magnetite in the unweathered Tomstown Formation or Gatesburg Formation, was probably precipitated from solution when the slightly acid ground water permeated the unleached 

carbonate beds of either the Tomstown or Gatesburg. Thus, the iron 

ore deposits in South Mountain mined during the mid- to late-19th 

century and the Scotio iron ore deposits mined during the late-19th 

and early-20th centuries, were formed by supergene enrichment and 

are similar in origin to those in Virginia (Lesure, 1957, p. 98).

It is difficult to determine the age of the white clay deposits in 

Pennsylvania. Undoubtedly the age of all the clay deposits is about 

the same because the climatic conditions conducive to katamorphic 

alteration were rather uniform throughout the entire region. The 

clay deposits near Kunkletown and Saylorsburg are southwest of a 

Wisconsin glacial terminal moraine. No clay deposits are known 

northeast of the moraine. Therefore, the clay deposits formed before 

the Wisconsin glaciation, and those northeast of the moraine were 

stripped away during glacial advance.

The interpretation by Pierce (1965) indicates that the Great 

Valley and Valley and Ridge provinces of Pennsylvania have been 

exposed to subaerial erosion and weathering since Cretaceous time, 

and possibly before. This establishes a possible age for the beginning 

of katamorphic alteration by weathering. Griffiths and others (1956) 

agreed that tropical weathering of central Pennsylvania during Cretaceous time is the most probable date for the beginning of the 

formation of the clay deposits. It is also reasonable to believe that the 

clay deposits are a product of prolonged weathering over several 

million years and that large amounts of unprotected residuum have 

been removed.
WHITE CLAYS OF PENNSYLVANIA D37

CONCLUSIONS

The production of white clay in Pennsylvania has declined during the past 20 years. White clay is still being mined at Toland, 

Cumberland County, by the Philadelphia Clay Co. and near Kunkletown, Monroe County, by the Universal Atlas Co. Clay from these two 

deposits is being used to make white cement, and both deposits have 

many years of reserves at their current rate of production. Between 

Kunkletown and Saylorsburg, additional silty clay deposits are 

known on strike with the present pits. At Toland, additional clay is 

present at depth and also on strike with the present pit both east and 

west. The other clay deposits are not being mined currently because 

the demand for high-grade refractory clay brick has dropped. The 

known clay deposits in the Gatesburg Formation of central Pennsylvania do have some reserves, and there are probably a few undiscovered clay deposits, but, owing to current lack of demand, both 

mining and prospecting are at a standstill.

The idle clay pits may become sites for storing hazardous waste. 

Inert solid-waste material would not cause any problem to the environment, but liquid and chemical waste material would be hazardous 

because of the origin of the clay deposits. The clay deposits are 

composed of silty clay and clayey silt derived from katamorphic 

alteration of limestone or limy shales or phyllites. The alteration was 

the result of ground water percolating through the rock causing the 

formation of saprolite. Because the saprolite is very porous, any 

attempt to store liquid or chemical waste in it would contaminate the 

ground water and result in a hazard to the environment.

REFERENCES CITED

Butts, Charles, Swartz, F. M., and Willard, Bradford, 1939, Geology and mineral 

resources, Tyrone quadrangle [Pa.]: Pennsylvania Geological Survey, 4th ser., 

Topographic and Geologic Survey Atlas of Pennsylvania 96,118 p.

Epstein, J. B., and Epstein, A. G., 1967, Geology in the region of the Delaware to 

Lehigh Water Gaps, Field Conference of Pennsylvania Geologists 32d, East 

Stroudsburg, Guidebook: Harrisburg, Pa., Pennsylvania Geological Survey, 89 p.

Epstein, J. B., and Hosterman, J. W., 1969, Residual clay deposits in rocks of Early 

and Middle Devonian age near Kunkletown, Pennsylvania: U.S. Geological Survey Professional Paper 650-D, p. D94-D105.

Freedman, Jacob, 1967, Geology of a portion of the Mount Holly Springs quadrangle, 

Adams and Cumberland Counties, Pennsylvania: Pennsylvania Geological Survey, 4th ser., Progress Report 169, 66 p.

Gray, Carlyle, and others, 1960, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., scale 1:250,000.

Griffiths, J. C., Bates, T. F., and Shadle, H. W., 1956, Guide to field trip of Fourth 

National Clay Conference clay minerals in sedimentary rocks, in Swineford, 

Ada, ed., Clays and Clay Minerals: National Research Council Publication 456, p. 

1-20.
D38 CONTRIBUTIONS TO GEOLOGY OF MINERAL DEPOSITS

Grim, R. E., 1953, Clay mineralogy: New York, McGraw-Hill, 384 p. 

Hosterman, J. W., 1969a, Clay deposits of Spokane County, Washington: U.S. Geological Survey Bulletin 1270, 96 p. 

Hosterman, J. W., 1969b, White clay deposits near Mount Holly Springs, Cumberland

County, Pennsylvania: U.S. Geological Survey Professional Paper 650-B, p.

B66-B72. 

Hosterman, J. W., Scheid, V. E., Alien, V. T., anrd Sohn, I. G., 1960, Investigations of

some clay deposits in Washington and Idaho: U.S. Geological Survey Bulletin

1091,147 p. 

Leighton, Henry, 1934, The white clays of Pennsylvania: Pennsylvania Topographic

and Geologic Survey Bulletin 112, 19 p.

___1941, Clay and shale resources in Pennsylvania: Pennsylvania Geological Survey, 4th ser., Bulletin M23, 245 p. 

Lesure, F. G., 1957, Geology of the Clifton Forge iron district: Virginia Polytechnic

Institute, Agricultural Extension Service Bulletin 118,130 p. 

Moore, E. S., 1922, White clay deposits in central Pennsylvania: Pennsylvania Bureau

of Topographic and Geological Survey Bulletiiv45, 7 p. 

Munsell Color Company, 1954, Munsell soil color chart: Baltimore, Md., Munsell Color

Co., Inc. 

Peck, F. B., 1922, White clay deposits at Saylorsburg, Monroe County, Pennsylvania:

Pennsylvania Bureau of Topographic and Geological Survey Bulletin 40, 8 p. 

Pierce, K. L., 1965, Geomorphic significance of a Cretaceous deposit in the Great

Valley of southern Pennsylvania: U.S. Geological Survey Professional Paper

525-C, p. C152-C156. 

Ries, Heinrich, and Bayley, W. S., and others, 1922, High-grade clays of the eastern

United States, with notes on some western clays: U.S. Geological Survey Bulletin

708, 314 p. 

Rose, H. J., Jr., Adler, Isidore, and Flanagan, F. J., 1962, Use of LaaOs as a heavy

absorber in the X-ray fluorescence analysis of silicate rocks, in Geological Survey

Research 1962: U.S. Geological Survey Professional Paper 450-B, p. B80-B82. 

Rose, H. J., Jr., Cuttitta, Frank, Carron, M. K., and Brown, Robena, 1964, Semimicro

X-ray fluorescence analysis of tektites using 50-milligram samples ,,mGeological

Survey Research 1963: U.S. Geological Survey Professional Paper 475-D, p.

D171-D173. 

Stose, G. W., 1907, White clays of South Mountain, Pennsylvania: U.S. Geological

Survey Bulletin 315-1, p. 322-334. 

___1953, Geologic map of the Carlisle quadrangle, Pennsylvania: U.S. Geological

Survey Geologic Quadrangle Map GQ-28.