Pegmatites of the 

Middletown Area 

Connecticut

GEOLOGICAL SU R V EY BULLETIN 1042- Q

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

CONTRIBUTIONS TO ECONOMIC GEOLOGY

PEGMATITES OF THE MIDDLETOWN AREA, CONNECTICUT

By FREDERICK STUGARD, JR.

ABSTRACT

The pegmatites of the Middletown area in Connecticut have been mined almost 

continuously for feldspar and muscovite mica since about 1865. Pegmatites in 

this and other areas have recently become the subject of renewed interest because 

they are the potential source of beryl, the ore mineral of beryllium. From 1948 

to 1950 the Geological Survey studied and mapped the pegmatites in an area of 

about 58 square miles near Middletown. The primary objectives of the mapping 

were to determine beryllium resources of the Middletown area and to ascertain 

relations of beryl-bearing pegmatites to non-beryl-bearing pegmatites and to 

type of wall rock.

More than 330 concordant and discordant pegmatites were examined within 

the mapped area. The pegmatites cut the metasediments of the Bolton schist 

of pre-Mississippian(?) age and, in ascending order of sequence, mafic gneisses, 

the Glastonbury granite gneiss, Maromas granite gneiss, and Monson gneiss. 

The position of these formations in the stratigraphic column cannot be determined with accuracy; their maximum age is indicated by their relation to the 

pegmatites, which have been dated by uranium- and thorium-lead ratios as about 

260 million years old, presumably Mississippian.

The Bolton schist includes middle- to high-rank mica-quartz schist of various 

compositions interbedded with minor quantities of quartzite, diopside- and 

hornblende-bearing marble, and hornblende-bearing schist and gneiss. The 

mafic-.gneiss is predominantly hornblendic gneiss and schist with subordinate 

mica schist and light-colored feldspathic gneiss. These metasediments are cut 

by the Glastonbury granite gneiss, a gray to pink medium- to coarse-grained 

porphyritic gneiss; by the Maromas granite gneiss, a gray medium-grained 

biotite orthogneiss; and by the Monson gneiss, a banded to massive mediumgrained biotite granodiorite gneiss. .

The metamorphic rocks in the northern part of the Middletown area dip westward, but in the southern part the Bolton schist is bowed up by the Monson 

gneiss into a dome. Between these areas the rocks show evidence of intense 

folding and overturning. The western part of the area is covered by fanglomerate, conglomerate, sandstone, and siltstone of Triassic age, bounded by normal 

faults. An east-trending fault of indeterminate age probably offset the meta? 

morphic and .igneous.rock units in the area near Great Hill.

.The pegmatites are composed essentially of perthite, quartz, plagioclase, and 

muscovite. The common accessories are tourmaline, beryl, garnet, and biotite. 

The pegmatites have been divided into four groups based on the content of
614 CONTRIBUTIONS TO 'EOONOMDC GEOLOGY

plagioclase feldspar: those with less than 40 percent of plagioclase, with and 

without beryl; and those with more than 40 percent of plagioclase, with and 

without beryl. About 42 percent of the pegmatites contain more than 40 percent plagioclase, and 58 percent of them contain less than 40 percent of plagioclase.

Most of the pegmatites are nearly homogeneous bodies with a grain size from 

about 1 to 4 inches. They have a finer grained border zone, 1 to 6 inches thick, 

with a mineral composition similar to the main part of the body. This type of 

pegmatite is of limited economic value. About 25 percent of the pegmatites, 

'however, show a systematic variation in mineral composition from the walls 

inward. Units of differing mineralogic or textural characteristics are usually 

richer in perthite, albite, muscovite, or quartz. The grain size increases from the 

walls to the center of the pegmatite. As many as five distinct units, or zones, 

parallel to the pegmatite wall-rock contact have been noted in an individual 

pegmatite. In some pegmatites fracture-filling units of quartz and perthite cut 

the zones. No replacement units were recognized.

The ratio of concordant to crosscutting pegmatites is almost 3 to 1. The 

pegmatites appear unaffected by regional metamorphism, but they have deformed 

their wall rocks. The wall rocks have been altered near the pegmatites by the 

addition of tourmaline, muscovite, albite, and beryl.

The total resources of beryl, sheet and scrap muscovite, and feldspar are 

unknown because of poor exposures and limited development. Feldspar reserves 

are adequate to continue mining on the present scale for many years. No beryl 

deposits capable of sustaining an operation for beryl alone have been discovered, 

but rock containing 0.1 percent beryl or more is available in sufficient quantities 

for milling if future technical development makes its use desirable. Additional 

sheet and scrap mica can be produced profitably only if prices are much higher 

than during World War II.

INTRODUCTION

The pegmatites of the Middletown area of central Connecticut have 

been mined almost continuously since about 1865 for feldspar and for 

muscovite mica as a byproduct. Pegmatites in this and other areas 

have recently become the subject of renewed interest because they are 

the potential source of beryl, the ore mineral of beryllium.

When strategic uses were found for beryllium late in World War II 

(Smyth, 1945, p. 23, 24, 28, 42, 43, 48, 83-84), the U. S. Geological 

Survey undertook a study of potential sources of beryllium ore. 

Pegmatites of the Middletown area were studied and mapped during 

1948-50. These pegmatites form a large but very low-grade source of 

beryllium which may be utilized in the future if economic conditions 

make it profitable to separate the beryl from the feldspar, quartz, and 

mica of the rock. The average beryl content of pegmatite rock in the 

Middletown area is probably between 0.1 and 0.2 percent (0.02 percent 

BeO), although only a fraction of that quantity can be observed.

The pegmatites occur in a hilly terrain of metamorphic rocks of 

Paleozoic age east of a lowland developed on sedimentary rocks. 

These pegmatites are essentially granitic in composition and form a 

vast reserve of feldspar, quartz, and scrap mica. The Middletown
PEGMATITES OF THE MTDDiLETOWN! AREA, COKN1ECTTCUT 615

area includes most of the Middle Haddam map quadrangle (7 K-minute) 

and 15 square miles in the southwestern part of the Glastonbury 

quadrangle (fig. 59).

73" 72'

FIOTTBE 59. Index map of Connecticut showing Mlddletown area.

The Middle Haddam quadrangle is immediately east of the cities of 

Middletown and Portland in Middlesex County; the Glastonbury 

quadrangle, north of the Middle Haddam quadrangle, extends into 

'Hartford County. Access to the district is provided by a close network 

of hard-surface roads. The major highways crossing the area are 

U. S. Route 6A, and State Routes 2, 16, 17, and 151. The Airline 

division of the New York, New Haven, and Hartford Railroad crosses 

the area from east to west.

FIELDWORK

The total area mapped is about 58 square miles and covers part of 

the towns of Glastonbury, Portland, Middletown, East Hampton, 

and Haddam. The primary objectives of the mapping were to determine beryllium resources of the Middletown area and to ascertain 

relations to beryl-bearing pegmatites to non-beryl-bearing pegmatites 

and to the type of wall rock.

The areal geology of the Middletown area (pi. 56) was mapped on 

1:12,000 enlargements of the l:31,680-scale U. S. Geological Survey 

topographic maps of the Glastonbury and Middle Haddam quad*
616 CONTRIBUTIOSNIS TO ECONOMIC GEOLOGY

rangles. The pegmatites on this map were grouped according to the 

content of plagioclase, which was determined by megascopic examination supplemented by refractive-index determinations. A map of the 

pegmatite at the Hale quarry was made on the scale of 1 inch to 40 

feet, and the dumps of three of the largest pegmatite quarries (Hale, 

Howe, and Strickland-Cramer) were sampled and spectrographically 

analyzed for beryllium. Thin sections of the most characteristic rock 

fabrics and compositions were studied. Specific gravity of rock 

hand specimens was measured on a Penfield beam balance.

PREVIOUS WORK

The first geological survey of Connecticut was commissioned by the 

State legislature and carried out in two parts. Shepard (1837) reported 

on the mineral wealth of the State, and Percival (1842) published a 

State geologic map. Both Percival's map and its successor by Gregory 

and Robinson (1907) show a division of the metamorphic rocks in the 

Middletown area.

The metamorphic rocks in the Middletown area were described by 

Westgate (1902, written communication), Foye (1949), Digman (1950), 

arid Mikami and Digman (1957). The sedimentary rocks of the central lowland of Connecticut, which form the western part of this area,

-were mapped by Davis (1898) and Krynine (1950). Longwell (1937) 

studied the Triassic boundary fault that transects the pegmatites and 

metamorphic terrain.

Pegmatite studies hi Connecticut began with the discovery of rare 

minerals in the western part of the State (Brush and Dana, 1878, p. 

33-46). Numerous early articles described and named unusual pegmatite minerals, but the first systematic contribution to the mineralogy 

of pegmatites in central Connecticut appeared in 1902 (Bowman, 

1902).

Before World War I the U. S. Geological Survey and the Bureau of 

Mines made studies on the economic geology of pegmatites (Bastin, 

1910; Watts, 1916), including the deposits of central Connecticut. 

During the twenties and thirties guides for mineral collectors in the 

area were compiled (Shannon, 1920; Foye, 1927; Zodac, 1937; Gillette, 

1937), and numerous articles described the minerals from various 

quarries.

Between 1926 and 1939 Schairer (1926, written communication), 

McKnight (1926, written communication),-Jenks (1935), and Russell 

(1926, written communication), studied phases of the mineralogy of 

pegmatites in the Middletown area. Schairer and Jenks studied the

 Strickland-Cramer pegmatite on Collins Hill and outlined a paragenesis of the minerals based on the theory of metasomatic replacement
PEGMATITES OF THE MLDDLETOWNl AREA, CONNECTJiCUT 617

of an originally simple granitic pegmatite. McKnight studied several 

pegmatites in some detail, and Russell made an outline map showing 

the location of numerous pegmatites.

Economic studies of Connecticut pegmatites, including the Middletown area, began with the descriptions of mica deposits by Sterrett 

(1923). R. J. Ordway (1942, written communication), examined 

many pegmatites for their potential mica production, on behalf of the 

Connecticut Development Commission. During World War II the 

U. S. Geological Survey investigated hi this area many pegmatites 

containing sheet mica and beryl (Cameron and Shainin, 1947; Cameron 

and others, 1953). This work consisted of detailed structural and 

mineralogic studies on numerous pegmatite bodies being mined at 

that tune. At that time core drilling was done by the United States 

Bureau of Mines to explore some of the pegmatites (Boos, Maillot, 

and Mosier, 1949).

ACKNOWLEDGMENTS

As part of the government program for investigation of domestic, 

beryllium resources, geologic mapping of pegmatites in the Middletown area hi central Connecticut was undertaken by the U. S. Geological Survey, partly in cooperation with the Division of Raw Materials 

of the U. S. Atomic Energy Commission.

. Mr. Edwin W. Tooker served ably as field assistant during the field 

seasons of 1948 and 1949. Mr. Robert V. Cushman of the U. S. 

Geological Survey, permitted mention of data not yet published in 

connection with a short stretch of buried river channel in the Middle 

Haddam quadrangle. Spectrographic analyses were made by Miss Janet 

D. Fletcher of the U. S. Geological Survey. Yale University furnished the writer office space and laboratory facilities during the 

preparation of the report. The writer is grateful to Professor Adolph 

Knopf for much helpful advice during the course of the work. Particular thanks are due Professor J. W. Peoples, of Wesleyan University, 

for making available numerous thin sections and other data. Dr. E. L. 

Troxell, Director of the Connecticut Geological and Natural History 

Survey, made available the unpublished manuscripts of Dr. Ralph 

Digman, the late Dr. W. G. Foye, and others. Professor R. F. Flint, 

of Yale, kindly permitted full use of manuscript maps from forthcoming publications showing the distribution of Pleistocene sediments; 

on the northern and eastern sides of the Connecticut River as far 

south as the village of Middle Haddam. The management of the, 

Eureka Mica Mining and Milling Co. kindly allowed examination; 

of the Hale quarry in Portland.

461639 5S
618 OONTRIBUTi'OOM'S TO 'ECONOMIC GEOLOGY

PHYSIO GRAPH Y

The terrain of the Middletown area represents two physiographic 

regions: the Connecticut Valley lowland, west of the Triassic boundary 

fault (pi. 56) and the eastern highlands of Connecticut, east of the 

Triassic boundary fault. The altitude ranges from slightly above sea 

level at the Connecticut River to about 730 feet at Great Hill. The 

cause of the abrupt deviation of the Connecticut River from the less 

resistant Triassic rocks of the lowland into the eastern highlands 

(Davis, 1898, p. 155-156) has been a long-debated problem. This 

change hi direction occurs within the area mapped, and the river 

continues across the structure of all rock units encountered to its 

mouth at Saybrook, Conn. The wide river valley formed on the 

Triassic rocks changes abruptly at the Straits (pi. 56) to a steepwalled gorge, where the river enters the White Rocks area of schist 

and gneiss.

Rice and Foye (1927) have summarized the regional evidence on 

the preglacial course of the Connecticut River above the Straits and 

believe that it coincided with the present channel of the Mattabesset 

River. The former course of the Connecticut River southward 

through the present site of Job's Pond is thoroughly discussed by 

Longwell and Dana (1932, p. 174). The area mapped as glacial outwash at this locality roughly delineates what is believed to be the 

position of the old river channel during glacial tunes. Evidence of 

the now-buried river channel has been found (Cushman, oral 

communication, 1948) by plotting the depths of bedrock from data 

obtained from records of the digging of water wells. The channel in 

the bedrock below the glacial drift extends from Gilders!eeve to Job's 

Pond. A well on the north side of William Street (pi. 56) 1,400 feet 

northeast of the Eureka Mill met bedrock 100 feet below sea level. 

The thickness of sand above the buried channel is more than 200 

feet, in contrast to the average thickness of till and stratified drift, 

which is about 19 feet (Palmer, 1920; WPA, 1938).

The cross-axial course of the Connecticut River might be explained 

by the following hypotheses: That the river channel through the 

straits is a consequent one, formed as an outlet from a higher basin; 

that by headward erosion the early Connecticut River cut through 

the ridge at the western edge of the eastern highlands to capture a 

southward flowing stream in the lowland; that the turning of the 

Connecticut River into the highlands was localized by faulting; or 

that the southeast reaches of the Connecticut River and other streams 

were superposed from an unconformable cover of sedimentary rocks. 

Davis (1898, p. 155-156) concluded that the most probable origin 

was by superposition from Cretaceous coastal plain strata similar to 

those on the northwest side of Long Island. Davis's conclusion has
PEGMATITES OF THE MIDDUETOWN AREA, OONNEICTICUT 619

been strengthened by the finding of a log of Cretaceous age in the 

glacial drift several miles from the straits (Dunbar and Flint, 1939.)

GEOLOGY

The pegmatites (pi. 56) in the Middletown area intrude a sequence 

of metasediments of various compositions (Bolton schist and a unit: 

called mafic gneiss), a biotite gneiss (Glastonbury granite gneiss), a : 

granitic orthogneiss (Maromas granite gneiss), and a tonalitic ortho-, 

gneiss (Monson gneiss).

The Bolton schist is predominantly mica schist with interbedded. 

layers of quartzite and amphibole-bearing gneiss. The Bolton schist 

is probably early Paleozoic in age. The mafic gneiss group is believed 

to be largely tuffaceous in origin; this gneiss is characterized by the 

presence of hornblende. Mafic gneiss crops out in a sinuous band 

east of the Maromas granite gneiss, extending northward to its. 

intersection with the Triassic boundary fault. The Glastonbury 

granite gneiss is an elongate body of biotite gneiss, 4% miles in maximum width, extending from Great Hill northward into Massachusetts. 

It is not clear whether this gneiss is actually an intrusive rock as the 

name implies or a metamorphosed sedimentary formation. The. 

geologic sections (pi. 56) could best be drawn, it was found, on the. 

basis of an intrusive origin for the unit.

The stratigraphic thickness of the metasedimentary formations in 

the Middletown area cannot be measured, owing to the absence of key 

horizons and the intensity of folding apparent in the exposures.: 

The Bolton schist is estimated to be 1,400-4,300 feet thick, and the 

mafic gneiss, 2,000-3,000 feet thick. The estimates are based on the 

geologic sections (pi. 56).

The Maromas granite gneiss intruded the Bolton schist in pre-. 

Mississippian tune and forms a small and well-defined stock in the 

central part of the area. Another orthogneiss of tonalitic composition, called the Monson granodiorite by Emerson (1917, p. 241-243), 

forms the northernmost part of the Killingworth intrusive dome 

(Mikami and Digman, 1957) shown in part at the lower edge of plate 

56. This intrusive rock of pre-Mississippian age, unlike the Maromaa 

granite gneiss, has converted the adjacent Bolton schist into a migmatite. An extension of the Monson gneiss has been traced continuously from the east side of the Killingworth dome (the southern 

part of the area shown in pi. 56) to the type area in the Monson quarry 

in Massachusetts. East of Middle Haddam the Monson gneiss has 

an indefinite contact with the Hebron gneiss.

The unmetamorphosed sedimentary rocks west of the Triassic 

boundary fault are the uppermost part of the Newark group of early 

Late Triassic age. Silty sandstone grades eastward into conglomerate
620 coNTRiBtmoasns TO ECONOMIC GEOIX>GY

and at the fault it becomes a fanglomerate. These sediments, like 

the crystalline rocks, are cut by dolerite dikes. Most of the Triassic 

formations in this area are covered by Quaternary sand, gravel, and 

alluvium (pi. 56).

Pegmatites cut all of these metamorphic and igneous rock units 

but are older than the Triassic sedimentary rocks and dolerite dikes. 

The largest pegmatites occur in the more fissile rocks, notably the 

Bolton schist, within which most pegmatites are concordant intrusions. 

The pegmatites within the Glastonbury granite gneiss are small concordant masses and large dikelike bodies that in general are nearly 

parallel to foliation of the enclosing rocks.

The geologic history of the area is summarized as follows: 

In pre-Mississippian(?) time sediments later metamorphosed into 

Bolton schist. Deposition of tuffs and other sediments, later metamorphosed to mafic gneisses; in Mississippian(?) time regional 

metamorphism began, accompanying the intrusion of Glastonbury 

granite gneiss(?) and decreasing in intensity during intrusion of 

Maromas granite gneiss and Monson gneiss. Intrusion of pegmatites 

followed; late Middle Triassic and early Late Triassic tune were 

characterized by normal faulting, deposition of the Newark group, 

and intrusion of dolerite dikes; in Cretaceous(?) time sediments 

similar to those of the coastal plain were deposited and eroded; in 

Pleistocene tune with the advent of glaciation ice-contact sand, 

gravel, and till were deposited, accompanied by changes in drainage 

and deposition of river terraces and alluvium.

BOLTON SCHIST

The Bolton schist (Percival, 1842, p. 229-233 and map) crops out 

as a narrow band in the northern part of the Middletown area and 

near the Straits in the Connecticut River (pi. 56) just east of Middletown, and it divides into two broader bands that enclose the northern 

end of the Killingworth dome. The west boundary of the unit is a 

westward-dipping normal fault of Triassic age. The narrow band of 

Bolton schist extending northward from Collins Hill to the viUage 

of South Glastonbury also is cut on the north by a Triassic fault. 

These two areas of schist are separated by a narrow belt of mafic 

gneiss; the easternmost body of schist can be followed northward 

beyond the area shown in plate 56 to the type locality at Bolton 

Notch, Conn.

The Bolton schist is dominantly mica-quartz schist of highly 

variable composition (table 1) that locally contains appreciable quantities of garnet, hornblende, and kyanite. Quartzite crops out at 

Great Hill; amphibolite, at many places south of the Connecticut 

River; and impure marble, in three observed localities. : Lenses of
PEGMATITES OF THE MTD.D.LETOWN1 AREA, CON^lEiCTJCTUT 621

massive quartz, conformable with the foliation, occur throughout the 

formation. They are from a fraction of an inch to about 2 feet thick 

and usually taper to thin seams at their ends. Tourmaline and beryl 

crystals as much as 4 inches in diameter are present in the schist near 

some pegmatites. Gneissic textures are locally developed in some, 

places.

The best exposures of marble beds in the Bolton schist are in thtf 

west end of a road cut on the river road on the south bank of the 

Connecticut River, just east of the Triassic boundary fault; these beds 

are individually only a few inches thick. Other lime-rich beds are 

isoclinally folded for about 50 feet in the Airline railroad cut 200 feet 

east of the State Route 17 overpass. In the woods south of the 

Straits there are other lime-rich beds several inches thick. The 

thickest quartzite beds in the Bolton schist, about 200 feet thick, 

crop out as cliffs at the south end of Great Hill; the quartzite is nearly 

massive at the south end, but a few hundred yards farther north is a 

crumpled mica-quartz schist containing about 20 percent of muscovite 

And small quantities of kyanite, rutile, and zircon.

Most of the observed .modes of the Bolton schist (table 1) are of 

upper middle metamorphic rank, corresponding to the almandine 

garnet zone of British usage (Tilley, 1925, pp. 100-109), but there 

are several outcrops of .higher rank. The upper middle metamorphic 

rank is marked in the Bolton schist by ubiquitous garnet and brown 

biotite, and in a few places, such as the southeast face of Great Hill, 

by small staurolite crystals scattered in quartz-biotite schist. Higher 

rank metamorphism is noted on the western slope of Collins Hill 

where blades of kyanite, % by 3 to 4 inches, are common in kyanitebiotite-quartz schist. The blue kyanite is confined to the 10 feet of 

schist immediately adjacent to the contact with a small plug of 

Maromas granite gneiss. Westgate (written communication, 1902) 

reports abundant, minute staurolite crystals in the Bolton schist along 

State Route 2, in a ravine at the eastern edge of the Glastonbury 

quadrangle. Westgate also found staurolite crystals, with a maximum size of % by 3 inches, in a quartz-biotite-garnet-staurolite schist 

in the hills just west of Pocotopaug Lake, in the Middle Haddam 

quadrangle.

Sillimanite and its varietal form, fibrolite, occur with the quartzite 

at Great Hill. The presence of sillimanite, and the relatively coarse 

grain of the rock, suggests that the entire Bolton schist may be of 

high metamorphic rank and that sillimanite occurs only in the schistose 

parts of the quartzite because quartzite is the only rock in which the 

A1203 content exceeds the combined CaO, K20, and Na20 content.

Mylonitic or cataclastic textures were observed in thin sections of 

specimens from several localities, indicating that the. Bolton schist
TABLE 1. Modes of the Bolton schist 

[Percentages of minerals based on visual estimates; X Indicates less 

Location

Roadside at south end, Collins Hill,

Portland. 

Near Job's Pond, 25 feet north U. S.

Route 6A.

One mile northwest of Bear Hill, 

Middletown.

village, 1,000 feet east of State Route 

17.

bury, 1,400 feet east of Still Hill 

Cemetery. 

Southwest of Benvenue village, Middletown.

Hampton boundary.

South-southeast of Great Hill, 0.3 

mile east of road through Cobalt.

Hill, near Pocotopang Lake.

Hampton.

of Bear Hill, Middletown.

Hill, just west of Hubbard Pond.

Creek on east-west road leading to 

Asylum Reservoir 2.

Two miles north of Higganum, Conn.,

beside railroad, just south of marsh.

W mile north of East HamptonHaddam boundary.

Rock types

Fine-grained quartz-feldspar-biotite schist. 

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

Medium-grained biotite schist...

spar-biotite schist.

lonitic.

spar-biotite schist. 

Medium-grained biotite-quartz

schist.

schist. 

Medium-grained quartz-feldsparbiotite-epidote pneiss.

ampbibolite schist.

gneiss.

Medium-grained amphibole

schist.

with tonalite in Monson 

gneiss.

Specific 

gravity

2.73

2.68

2.67

2.65

Quartz

70

67

40

40

42

40-45

20

09

80

40

60

63

10

35

45

45

25

30

12

Microcline

10

2

5

40

10

15

15

10

3

13

Plagloclase

20 (Anjs-so)

10 (Anss-ja)

25 (Anjs-M)

35 (Ansi-3!)

10 (An2i-so)

X

10 (An«)

30 (Ann)

25 (An*s-3j)

60 (Anjj-so)

60 (Anw-zs)

7 (Anno)
cut, 300 feet northeast of Intersection of State Route 17 with U. S.

Route 6A, Portland.

mas granite gneiss, southeast of 

Benvenue village.

gneiss, northwest of M aromas Cemetery.

granite gneiss in brook below Benvenue quarry, Middletown.

gneiss north of Maromas Cemetery.

gneiss near northern boundary of 

gneiss, at end of old railroad switchback.

Near contact of Bolton schist with 

Maromas granite gneiss, old quarryrailroad switchback,_ Benvenue 

quarry.

Layer at contact with Glastonbury

granite gneiss, Carr Brook at north 

end of Collins Hill, Portland.

asslc boundary fault.

1 lime-silicate rock.

vite gneiss.

garnet schist.

staurolite schist.

gneiss.

gneiss.

garnet-trcmolite gneiss.

garnet gneiss.

mlcrocline rock.

ite.

grained muscovite-quartz 

schist.

2 77

60

1(1

10

20

15

qn

35

80

55

8ft-£K

45

40

28:(An

4(An
624 CONTRIBUTIONS TO ECONOMIC GEOLOGY

has been subjected to widespread deformation. All outcrops of the 

Bolton schist within about 300 feet of the Triassic boundary fault 

have also been affected by faulting and are composed of quartz, 

calcite, chlorite, and sericite, with or without feldspar; similar rocks 

have been found near the Triassic boundary fault outside the Middletown area (Digman, 1950).

The conspicuous compositional layering of the Bolton schist is 

everywhere parallel to the foliation. This parallelism between foliation and an earlier S-plane probably represents a parallelism between 

foliation and the original sedimentary bedding. There is a secondary 

cleavage across the foliation of Bolton schist outcrops on Straits Hill, 

but elsewhere the foliation parallels bedding in exposures. An 

exposure of mica-quartz schists in the railway cut just west of Route 

6A and east of Cobalt shows dragfolding and mica crenulations that 

indicate intense folding, but the detailed structure cannot be deciphered without subsurface information. The Bolton schist is of 

metasedimentary origin and is prepegmatite in age; that is older 

than 260 million years (pre-Pennsylvanian).

MAFIC GNEISSES

Mafic gneisses crop out in an S-shaped band about 0.3 mile wide, 

extending from South Glastonbury village about 12 miles southward. 

The outcrops are sparse, small, and weathered except for a few road 

cuts along U. S. Route 6A and State Route 17. As shown by the 

modes in table 2, the mafic gneisses are mostly amphibolitic gneisses 

and schists, interbedded with subordinate layers of biotite schists and 

gneisses, and minor quantities of granulite, quartzite, gabbroic gneiss, 

microclme-bearing gneiss, and diopside-garnet-hornblende gneiss.

The mafic gneisses commonly contain either microcline, oligoclase, 

or andesine feldspar associated with quartz. The hornblende and 

biotite grains are chloritized in some samples. Pyrite is a fairly 

common accessory, and sillimanite was found in two thin sections. 

The northern extension of the mafic gneisses have in general a moderate 

to steep westerly dip. It can be seen in plate 56, however, that the 

southern part of the formation is characterized by moderate to steep 

easterly dips. This reversal of dip in the southern part of the area 

is around the edge of a domal structure of Monson gneiss (the Killingworth dome).

The presence of mica schist beds or lenses within the mafic gneisses 

suggests a pelitic sedimentary origin for the group. The mafic gneisses 

are prepegmatite in age and consequently older than 260 million 

years. These gneisses are also probably older than the Maromas 

granite gneiss, as two small bodies of Maromas seem to be intrusive 

and lie within the mafic gneisses.
TABLE 2. Modes of the mafic gneisse

[Percentages of minerals based on visual estimates; X indicates l

Location

Just south of New Haven Railroad, between 

Great Hill Pond and the river, Portland 

(feldspathic stringer). 

On east-west road, between Job's Pond and 

Collins Hill, Portland* 

North of Carr Brook, on north-south road, 

southeast of Fogelinarks Corners, Porttend. 

North of Carr Brook, east of State Route 17 

Road cut on Route 6A, northeast of Paper 

Rock.

Road cut on east side State Route 17, 0.9 

mile north of Glastonbury-Portland line.

Road cut on west side State Route 17, 0.36 

mile north of Glastonbury-Portland line.

Road cut on east side State Route 17, 1.1 

miles north of Fogelmarks Corners. 

Near second road intersection west of 

Haddam Neck village.

Beside brook in Middle Haddam village....

East Bank Connecticut River, 0.8 mile south 

of Middle Haddam village. 

East bank Connecticut River, just south of 

Middle Haddam landing. 

One and one-third miles east of Connecticut 

River, Y± mile south of East-HamptonHaddam line. 

Airline Railroad, cut north of Paper Rock, 

Portland. 

South side Airline Railroad, \\b miles west 

of Cobalt station. 

Roadside at bottom of bill, 1 mile southeast 

of Job's Pond.

Road cut on north side Route 6A, north of 

Paper Rock, Portland.

Between Airline Railroad and Route 6A, 

north of Paper Rock, Portland.

Rock types

Amphibolite..-- _______ ......

Feldspathic stringer In amphibolite

Microcline-quartz rock __ ..

[Fine-grained chloritized horn- 

\ blende gneiss.

Fine-grained microcline-biotitehornblende gneiss. 

Diopside-garnet-hornblende gneiss.

[Medium-grained plagioclase1 quartz-hornblende gneiss. 

| Medium-grained quartz-plagio- 

[ clase lens in gneiss.

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

Contorted, Medium-grained bio- 

[ tite schist.

Specific 

gravity

2.72 

2.72

2.88

2.63 

2.82

2.62 

2.63

2.89

2.83 

2.76

2.70

2.59 

2.62

2.65

Quartz

24

5

10 

20

25 

83

50

30 

3 

30 

60

17 

35

55-57 

60 

49

39

65 

35

65

Microcline

30

X

86-88

52-54 

5

25 

20 

30

39 

25

5

P

70 

33 

2-4 

40

40 

1

17 

10 
entrance to St. Clement's Castle, Portland.

Portland.

fault.

ing Brook, Qlastonbury, 300 feet east of

gneiss.

 { grained feldspar-quartz gneiss.

2.73

2.61

2.66

35

40

25

50

30

5-7

55

55

46

30
PEGMATITES OF THE MIDDkETOWlSn AREA, CONOTCTtHCUT 627 

GLASTONBURY GRANITE GNEISS

The Glastonbury granite gneiss (Westgate, written communication, 

1902; Rice and Gregory, 1906, p. 114-115 and map) extends (pi. 56) 

from Portland northward into Glastonbury with a maximum width 

of about 4% miles; it is reported to extend northward into Massachusetts with an average width of about 3 miles (Westgate, written 

communication, 1902; Emerson, 1917, p. 243; Keppel, 1941). Most 

of the outcrops of this rock in the Middletown area are small 

ledges in creeks and roadcuts or dip slopes on the western sides of 

hills. Nearly horizontal domal outcrops of Glastonbury granite 

gneiss form some hilltops; for example, Clark Hill and Belltown Hill. 

The largest exposure in the area is in the cliffs northwest of Belltown 

Hill. Large glacial boulders of this gneiss litter many fields.

The area of Glastonbury granite gneiss mapped (pi. 56) is almost 

the same as that mapped by Westgate 50 years ago. Westgate proposed the name Glastonbury granite gneiss at that time, but his 

manuscript remained unpublished, and the name came into use from 

the report by Rice and Gregory in 1906. A detailed study of this 

gneiss over a larger area was carried out by the Connecticut Geological 

and Natural History Survey in 1950 and 1951 and subdivisions of the 

formation have been mapped (Herz, 1955). In general, the Glastonbury granite gneiss is a gray to pink medium- to coarse-grained 

porphyritic gneiss.

Three varieties of Glastonbury granite gneisa underlie this area: 

a schistose facies along the west edge of the formation, a biotitic 

gneiss some with hornblende and some without and a granitic 

facies. Modes of samples from each facies are shown in table 3. 

The essential minerals include quartz, microcline or oligoclase-andesine, and biotite. Hornblende and epidote are the most common 

accessory minerals.

Except for the presence of euhedral epidote, the schistose facies of 

the Glastonbury granite gneiss is almost indistinguishable from the 

adjacent Bolton schist. This facies of the Glastonbury granite gneiss 

is characterized by a grain size of less than 1 millimeter and a shredded 

appearance of the biotite, which is chloritized in part. Some samples 

show cataclastic textures. The microcline, plagioclase, and biotite 

grains give a salt-and-pepper appearance to weathered outcrops. 

There is a rather abrupt transition eastward from the schistose facies 

to the biotite gneiss facies. Small exposures of the schistose facies 

can be found near the inferred contact with the Bolton schist (pi. 56).

The biotite gneiss facies characterizes the greatest part of the Glastonbury granite gneiss: a gray to pink medium- to coarse-grained 

porphyritic or porphyroblastic gneiss. Much of the exposed biotite 

gneiss is a flaser gneiss; that is, a gneiss containing coarse-grained
TABLE 3. Modes of the Glastonbury granit

[Percentages of minerals based on visual estimates; X indicates l

Location

Hanging- wall pegmatite (GottaWalden quariy), drill core.

bury.

bury, just south of old feldspar 

mill site.

Hill, Glastonbury.

2. near triangulation station 

419, Glastonbury.

Chestnut Hill Road, Glastonbury, north of Brainerd Pond.

Pond, one-eighth mile east of 

road.

south of road.

Reservoir.

Hill Pond, Portland.

northwest of Penfleld Hill, 

Poitland.

Rock types

i ' biotite-epidote gneiss.

sine -biotite -hornblende 

gneiss. Almost schistose.

hornblende gneiss.

homblende-epidote gneiss.

cline-biotite-epidote gneiss.

ioclase-microcline Baser ' 

gneiss.

1 cline-plagioclase gneiss, near 

| biotite-rich streak.

gneiss.

cline-biotite-epidote gneiss.

cline gneiss.

quartz-plagioclase gneiss^

gvanulite.

clase-quartz-chlorite schist.

Specific 

gravity

2.86

2.82

2.68

2.62

2.64

2.61

2.57

Quartz

38

53

40

40

50

45

30

40

15

55

55

55

31

50

45

15

Microcline

5

5

10

40

15

40

40

35

44

- 47

40

45

Plagioclase

23 (An3«)

35 (Anas)

40 (Ansz)

45 (Amo)

20 (Anw)

50 (An38)

21 (Ans»)

5-10 (Anw)

70

Mu

v

X

X

X
PEGMATITES OF THE MIDDLETOWN AREA, CONNECTICUT 629

lens-shaped aggregates of microcline or quartz, about 0.3 to 0.4 inch 

long, wrapped in biotite flakes. The flaser wedges out along foliation 

planes. The biotite gneiss facies has little "knots" of biotite plates, 

as do the other facies, and this is the most distinguishing feature of 

the Glastonbury granite gneiss. The biotite content is as much as 30 

percent in some places but averages 5-10 percent. Small amounts of 

microcline are present in almost every sample of this and the other 

facies of the Glastonbury granite gneiss although it is subordinate to 

quartz and plagioclase. Epidote or hornblende is the most important 

accessory mineral and occurs in almost all samples. The epidote 

grains are unaltered and occur within hornblende, biotite, the feldspars and as a fringe around some allanite crystals. Typical exposures 

of biotite gneiss are in the bed of Roaring Brook at South Glastonbury 

and in the cliffs northwest of Bell town Hill. A hornblendic variety of 

this facies was sampled in the drill cores from the hanging wall of 

pegmatite 386 (Gotta Walden quarry).

The last main facies of the Glastonbury granite gneiss in the Middletown area is the granitic facies. This nearly massive facies is exposed in several small quarries on Larson Hill (pi. 56) in Portland. 

The rock is white with black spots or "knots" of biotite and has an 

obscure foliation. Quartz, microcline, and biotite are the essential 

minerals (table 3) with less than 1 percent of any accessory. This 

rock represents a highly siliceous granite the original texture of which 

is obscured by the later metamorphism.

Within the Middletown area the Glastonbury granite gneiss strikes 

north-northeast and dips homoclinally 30°-45° W., except at its 

southeast end (pi. 56). The southeasternmost outcrops, on Larson 

Hill, dip southeastward; south of here the formation is not exposed 

and is probably cut off by an east-trending fault at Great Hill Pond. 

The fault believed to have cut off.the south end of this formation 

may continue beyond the Middletown area in a northeast direction 

(Herz, 1955).

The dips of the foliation suggest that the Bolton schist and the 

mafic gneiss have been cut off at depth (pi. 56, sec. B-B') by an 

intrusion of Glastonbury granite gneiss. Three bits of internal evidence also probably indicate an igneous origin for the Glastonbury 

granite gneiss: inclusions of Bolton schist within the Glastonbury 

granite gneiss on top of Collins Hill, dark oval biptite-rich patches 

or schlieren along foliation planes in the bed of Roaring Brook, and 

the occurrence of diopside at the contact with Bolton schist. The 

inclusion of Bolton schist can no longer be observed because since 

they were recorded by Westgate the area has been covered by dumps 

from the Cramer pegmatite mine. The schlieren are prominent features of the Glastonbury granite gneiss in the streambed a few him-
630 CONTRIBUTIONS TO ©003SFOMIC GEOILOGT

dred yards east of South Glastonbury, and they are probably incompletely digested remnants of Bolton schist. The contact relations 

of the Glastonbury granite gneiss can only be observed in this area 

at the site of a washed-out dam on Carr Brook on the north end of 

Collins Hill, Portland. Westgate (written communication, 1902) 

wrote the following description of the gneiss at this contact:

This rock differs from the normal Glastonbury hereabouts in the absence of 

epidote and in the small holding of biotite. Such foliation as is present is parallel 

to the contact with the schist, which is just west of the dam, and dips west. The 

foliation of the schist is also parallel to the contact. Separating the schist and 

.gneiss at the contact is a band, about two and a half feet in width, of rock of greenish color, containing hornblende, pyroxene, garnet, small grains of titanite, and 

feldspars and quartz. This peculiar band is sharply marked off from both gneisses 

and schist.

This contact layer of rock was thought to be a chilled, igneous contact rim (Westgate, written communication, 1902), but in view of its 

large calcite content (table 1) it probably represents a lime-rich layer 

in the Bolton schist that has been altered by contact metamorphism.

Some rock flowage at elevated temperatures, or "hot working" of 

the Glastonbury granite gneiss has certainly occurred where schlieren 

are present, It is possible that some of the apparently igneous phenomena might be alternatively explained as migmatization phenomena 

rather than igneous intrusion phenomena, if more detailed studies of 

the problem were carried out. In connection with the problem of 

origin, it should be pointed out that the proportion of quartz in many 

parts of the Glastonbury granite gneiss is much higher than that in 

other metamorphosed igneous rocks of New England, as for example 

those of New Hampshire (Billings, 1937, p. 500-501); this higher percentage of quartz is accompanied by a large percentage of dark minerals. The age of the Glastonbury granite gneiss is prepegmatite; 

that is, older than 260 million years, presumably pre-Pennsylvanian. 

(See pegmatite 3 in table 9.)

MAROMAS GRANITE GNEISS

The main body of Maromas granite gneiss occupies a roughly 

elliptical area, 1 by 3 miles, at the first bend in the Connecticut Kiver 

east of the Straits. This body of gneiss, elongate in a northwest 

direction, has a foliation with a general northwest strike and a dip 

of 6°-40° NE.; the average dip is about 25° NE. The best exposures 

of the Maromas granite gneiss are in the abandoned Maromas and 

Benvenue quarries (pi. 56).

A careful study of the petrography and origin of the Maromas 

granite gneiss was published hi 1899 by Westgate, who also proposed 

the name. The State geologic map (Rice and Gregory, 1906) presented the name as an accepted one.
PEGMATITES OF THE MIDDiUETOWN AREA, CONNIEICTXCIJT 631

The Maromas granite gneiss is a dark- to light-gray medium-grained 

rock of granitic composition (table 4), containing in places small and 

imperfect augen of white to pink microcline. The foliation ranges 

from obscure to good. As exposed in the quarries, the gneiss has a 

main set of joints, at 2-6 feet apart, parallel to the foliation; at least 

two other sets of joints cut the rock in the quarries. Biotite- and 

hornblende-rich streaks occur irregularly in the rock and are usually 

oval or elongate. Tabular bodies of microcline and quartz transect 

the biotite-bearing granite gneiss, both across and parallel to the 

foliation. These microcline and quartz bodies are 1-6 inches thick 

and contain less than 1 percent of dark minerals (mainly biotite and 

iron ores). Both the Maromas granite gneiss and the microclinequartz bodies are medium grained.

The quartz in the Maromas granite gneiss has highly serrate 

crystal boundaries and in places contains myrmekitic intergrowths. 

Both the microcline and plagioclase have small rounded inclusions 

of quartz. A few green hornblende grains are poikilitic. Brown 

biotite is the most abundant accessory mineral. A little of the biotite 

and part of the hornblende are chloritized. Sphene is present in most 

samples of the rock; allanite occurs in a few. Pyrite is the most 

abundant of the iron minerals. The foliation is produced by a roughly 

planar arrangement of both biotite and feldspars.

The tabular bodies of microcline-quartz rock that cut the Maromas 

granite gneiss are believed to be metamorphosed aplite dikes genetically connected with the granite gneiss. The metamorphic texture and 

medium grain size of these dikes contrast with the texture and grain size 

of the pegmatites in the area. Only one large pegmatite was mapped 

within the Maromas granite gneiss (pi. 56), and no contacts with the 

country rock were observed. The paucity of pegmatites within the 

Maromas granite gneiss is probably the result of the massive character 

of the rock.

Inclusions of mica schist, from a few inches to over 100 feet in 

length, occur within the Maromas granite gneiss near its contacts 

with the Bolton schist. Chilled borders of fine-grained, aplitoid rock 

an inch or two thick surround these inclusions in some places and 

cut across them hi others. There are also several larger exposures of 

aplite. The aplitic rock contains small idiomorphic garnets. The 

Maromas granite gneiss also contains minute red garnets within 

3 or 4 feet of its contact with the Bolton schist. These contact phenomena are best observed along the abandoned railroad grades leading 

southward from the River Road, Middletown, to the now idle Benvenue quarries.

Dark streaks in the Maromas granite gneiss, containing 10-20
TABLE 4. Modes of the Maromas granite 

[Percentages of minerals based on visual estimates; X Indicates 

Location

town.

village, near north-south road, Middletown.

mas quarry, Middletown. 

Middletown.

town.

East of Benvenue village, Middletown, near

Great Hill Pond Brook. Plug of Maromas

Old granite quarry on west side of Colllns Hill, 

Portland. Plug of Maromas granite gneiss

One-third mile east from Benvenue village,

Bock type

quartz-biotite gneiss.

spar-biotite gneiss.

microcline gneiss.

gneiss.

spar-biotite gneiss.

feldspar - hornblende - biotite 

, gneiss

hornblende gneiss.

cline-plagioclase gneiss.

cllne-plagioclase gneiss.

granitic gneiss.

biotite gneiss.

gneiss.

nite gneiss.

Contaminated border facies.

quartz-monwmite gneiss.

gneiss.

augen gneiss.

zonltic augen gneiss.

gneiss.

gneiss, xenolith(?).

Specific 

gravity

2.68

2.65

2.61

Quartz

45

45

55

40

dp.

45

40

15

30-35

35

35

50

40

35

55

30

41

45

30-35

45

40

Microcline

33

55

30

20

10

15

5

50

35

30-35

25

25

5

30

31

30

20

35

60

30

2
PEGMATITES' OF THE MIDDLETOWN) (AREA, CONNECTICUT 633

percent each of biotite and hornblende, are probably partly resorbed 

xenoliths of Bolton schist.

Two smaller separate bodies of Maromas granite gneiss which are 

exposed in the granite quarries on Collins Hill and Great Hill Pond 

Brook are of similar composition (table 4) to the main body of' 

Maromas granite gneiss but contain more augen and are slightly 

lower in specific gravity. These imperfect augen are 0.2-0.3 inch 

long and are pink in the center with white runs; they are composed 

of microcline and show a border of feldspar and quartz grams with 

sieve texture. These outcrops of granite gneiss are believed to represent two bodies of Maromas granite gneiss that were intruded along 

the contact between the Middletown gneiss and the Bolton schist. 

Like the rest of the Maromas granite gneiss, the rock from these 

exposures shows the effects of later straining; the quartz has strain 

shadows and serrate boundaries.

The mineral composition of the Maromas granite gneiss, as estimated for samples from various localities, is shown in table 4.

The foliation of the Maromas granite gneiss seems to be partly 

protoclastic and partly cataclastic. The relative importance of the 

two processes is not known. Because the rock has been recrystallized 

since its original formation, the degree of foliation owing to flowage 

during the initial crystallization of the original igneous rock cannot 

be ascertained. Because the biotite hi some places is broken and 

partly localized along boundaries between feldspar and quartz grains, 

it is probable that some of the foliation was produced by dynamic 

metamorphism. The foliation of the Maromas granite gneiss is not 

as well developed as that of other formations subjected to regional 

metamorphism (for example, the Glastonbury gneiss), and therefore 

it is probable that the Maromas granite gneiss did not undergo the 

full duration of regional metamorphism. The occurrence of one large 

microcline grain in each augen, with smaller feldspar grains around 

it, suggests that phenocrysts of potassium feldspar in the original 

granite were crushed and that the smaller feldspar grains formed 

around the coarse residual cores during deformation and recrystallization. For these reasons, the Maromas granite gneiss probably 

was regionally metamorphosed simultaneously with intrusion, and 

the foliation is both protoclastic and cataclastic in origin.

The composition of the Maromas granite gneiss, like that of parts 

of the Glastonbury granite gneiss, includes an abnormally high 

percentage of quartz. Unlike the Glastonbury granite gneiss, however, 

the Maromas granite gneiss shows no other indication of being of 

sedimentary origin. Evidence indicating an orthogneiss origin includes 

(1) the stocklike outline; that is, rounded, roughly elliptical; (2) the

461639 58 1
634 CONTRIBUTI'ONIS TO EJOONIOMIC GEOLOGY

contact cuts in places across the strike of the foliation of the enclosing 

schists; (3) the occurrence of inclusions, a few inches to many feet in 

length, which are believed to be either pendants or xenoliths of 

biotite schist, only near the borders of the Maromas granite gneiss; 

(4) the intrusion of two bodies of similar composition along the contact of the mafic gneisses' and Bolton schist at Great Hill Pond Brook 

and at Collins Hill; and (5) the occurrences of light-colored aplite 

at the contact with Bolton schist. Westgate (1899, p. 650-652) 

discussed this aplite and concluded that it is an endomorphic border 

facies of the intrusive Maromas granite gneiss. The aplite is more 

silicic and finer grained than the main part of the gneiss.

The Maromas granite gneiss intrudes Bolton schist and the mafic 

gneisses, and, therefore, is younger than those formations. Because 

at least one unmetamorphosed pegmatite cuts the Maromas granite 

gneiss, it is older than 260 million years.

MONSON GNEISS

The Monson gneiss was originally named the Monson granodiorite 

by Emerson (1917, p. 241-243 and map) for the rock occurring in the 

quarries at Monson, Mass. Both chemical analyses (Dale and Gregory, 1911, p. 259) and identification of all the feldspar as plagioclase 

(oligoclase to labradorite) indicate that at Monson the rock is a 

quartz diorite or tonalite rather than a granodiorite. The Monson 

gneiss is a banded to massive, medium-grained, biotite granodiorite 

gneiss. It crops out from Northfield southward through New Salem, 

Petersham, and Monson in Massachusetts, and across the towns of 

Strafford, Tolland, Vernon, Bolton, Glastonbury, Marlboro, East 

Hampton, Haddam, Chester, and Saybrook in Connecticut (Gregory 

and Robinson, 1907, map). This body of rock is about 2 miles wide, 

and its boundaries strike north, parallel to the near-vertical foliation. 

The areal extent of the formation in Connecticut has been extended 

from that originally mapped by Gregory and Robinson by correlation 

with the Haddam granite gneiss between the Middletown area and 

Long Island Sound (Mikami and Digman, 1957).

The Monson gneiss crops out in the Middletown area (pi. 56) in 

two separate localities: in a narrow belt along the eastern edge of the 

Middle Haddam quadrangle and in the Killingworth dome (Mikami 

and Digman, 1957) in the extreme southern part of the Middle 

Haddam quadrangle. These areas connect beyond the limits of 

the map (Mikami and Digman, 1957, map); the rock in both areas is 

a quartz diorite or tonalite gneiss. Exposures in the eastern belt 

of Monson gneiss are meager, mostly in roadcuts. Natural outcrops 

are weathered to a friable white rock hi which the biotite flakes 

show an obscure foliation.
PEGMATITES OF THE MIDtMJETOWN) AREA, CaJSn^CTTCUT 635

Amphibolite crops out as a discontinuous band as much as 100 feet 

wide about half a mile inside of, and parallel to the contact of, the 

Killingworth dome. North of this amphibolite layer, the tonalite 

gneiss is commonly thinly layered and contains 2-5 percent of hornblende ; south of the hornblendite layer, the rock is often quite massive 

and contains little or no hornblende.

The typical Monson gneiss of the Killingworth dome segment 

tends to be nearly massive tonalite gneiss, with a slight foliation 

produced by parallel biotite flakes. Garnets, less than 0.1 inch in 

diameter, are present, and the texture of the rock is granoblastic. 

The estimated mineral composition of the tonalite gneiss for various 

localities is given in table 5.

The tonalite gneiss exposed hi the roadcut on State Route 16 at 

Chestnut Hill in East Hampton is representative of the eastern belt 

of the formation. The rock is coarse grained, light gray, and layered 

with dark biotite-rich bands, 2-4 inches thick; the dark bands wedge 

out within 15 or 20 feet. The foliation is fan- to obscure, and the 

texture is granoblastic. Pink garnets occur in certain layers; some 

of these garnets are euhedral crystals about 0.1 inch in size, and 

many are skeletal growths enclosing quartz. All the quartz shows 

strain shadows, and some of the plagioclase shows inverse compositional zoning. Microcline is relatively rare in the eastern belt of 

the formation.

In the Killingworth dome the foliation of the Monson gneiss dips 

outward at a low angle. The strike of the banding within the Monson 

gneiss also commonly parallels the curved contact of the Killingworth 

dome. In the belt along the eastern edge of the Middle Haddam 

quadrangle, the dip of the foliation is much steeper, generally within 

20° of vertical. The type of folding indicated in the formation is 

shown in plate 56 (sec. C-C'}.

The high quartz content and compositional layering of the tonalite 

gneiss in the eastern part of the Middle Haddam quadrangle suggests 

metamorphism of sediments or tuffs. However, because both areas 

of tonalite gneiss in the quadrangle are continuous with the southernmost intrusive dome of New England (Mikami and Digman, 1957, 

map), it is believed that this variant may be the siliceous contaminated 

margin of a metamorphosed tonalitic intrusion.

The tonalite gneiss must be younger than the metasediments of 

the Bolton schist, and both units are cut by pegmatites believed to 

be 260 million years old. A class IV age determination made on 

allanite from a pegmatitic phase of the Monson gneiss at Greenwich, 

Mass., gave a maximum age of 370 million years (Marble, 1949, 

p. 19-20). If this determination is substantiated in the future, the 

Monson gneiss must be pre-Silurian in age.
TABLE 5. Modes of the Monson gne

[Percentages of minerals based on visual estimates; X indicates 

 Location

Roadcut on State Route 16 at Chestnut Hill,

East Hampton (garnetiferous layer).

corner of Middle Haddam quadrangle.

On road 1H miles north of MiddletownHaddam line, west side of river.

Route 9 and Connecticut River. 

East of Connecticut River, y\ mile north of

Haddam-East Hampton boundary.

miles north of Haddam-Middletown

boundary.

Railroad cut 1 mile west of East Hampton

village. 

South of Bear Hill, at south boundary of

Middle Haddam quadrangle.

Rock type

Layered gneiss __________

Garnetiferous layer, mediumgrained biotite gneiss. 

[Coarse-grained slightly layered

\ hornblende-biotite gneiss.

Biotite gneiss __________

Medium-grained biotite gneiss,

with minor microcline.

amphibollte within biotite 

gneiss.

xenollth.

Specific 

gravity

2.72

2.75

Quartz

63

55

57

66

30

52

49

52

50

40

77

Micro

dine
PEGMATITES OF THE: MIDDLETOWN AREA, CONNECTICUT 637 

PEGMATITES

Pegmatites (pi. 56) cut all the metamorphic rocks of the Middletown area. They are described on pages 640-665.

NEWARK GROUP

The western part of the Middletown area is covered by coarse 

conglomerates, sandstones (arkoses), and silts tones of Triassic age, 

separated by normal faults from the metamorphic rocks (pi. 56). 

The sedimentary rocks are mapped together as the Newark group.

Siltstone layers may be observed along the railroad at the extreme 

western edge of the Middle Haddam quadrangle (pi. 56) and adjacent 

to the mapped area at the abandoned brownstone quarries in the 

city of Portland. Bed outcrops of conglomeratic sandstone may be 

seen on Roaring Brook in Glastonbury, along the Airline railroad just 

north of U. S. Route 6A in Portland, on Duck Hill, and in the brook 

west of Indian Hill in Middletown. The transition from conglomeratic 

sandstone to boulder conglomerate can be seen by going eastward 

along William Street, Middletown. Outcrops of crushed and bleached 

Triassic rock can be observed within 100 feet of the Triassic boundary 

fault in a road cut on the south side of U. S. Route 6A in Portland.

The fine-grained part of the Triassic rocks in the Middletown 

area is composed of quartz, feldspars, and mica, stained with red iron 

oxides. Rock fragments of phyllite are common in the conglomerate 

but cannot be correlated with any rock cropping out hi the area 

mapped. At least 85 percent of the pebbles and cobbles in the 

conglomerates represent metamorphosed sediments similar to rocks 

in the Bolton schist. The phyllite pebbles and cobbles in the conglomerates represent metamorphosed sediments similar to rocks in 

the Bolton schist. The phyllite pebbles and cobbles are of a lower 

grade of metamorphism than the metasediments of the area to the 

east and may represent the upper parts of the Bolton schist that 

were removed during the Triassic period. This evidence suggests 

that a metamorphic terrain of low rank may have existed above the 

present medium- to high-rank metamorphic rocks, and possibly also 

above the present outcrop area of the Glastonbury granite gneiss.

No fossils were found in the red beds during the present investigation, but numerous fossil fishes, dinosaur tracks, and fossil reptiles 

have been found elsewhere within the Newark group; the age has 

been variously determined as late Middle Triassic or early Late 

Triassic (Lull, 1915, 1917; Colbert, 1946). The Triassic rocks in 

the Middletown area constitute the uppermost part of the Newark 

group and are, therefore, presumably Late Triassic age.

Krynine (1950, p. 30) divided the Triassic sedimentary rocks of 

southern Connecticut into three formations: the New Haven arkose,
638 OOlNTRIBUTI'OnSIS TO ECONOMIC GKOOLOGY

the Meriden formation, and the Portland formation. The Triassic 

rocks shown on plate 56 are part of the Portland formation.

Krynine (1950, p. 36) has shown that the heavy minerals from the 

lower part of the Portland formation consist of garnet (56 percent) 

and tourmaline (33 percent). Krynine determined that garnet 

comprises 72 percent and tourmaline 13 percent of the heavy-mineral 

concentrates in the upper Portland formation (Newark group on 

pi. 56). The tourmaline is mostly of the black variety, schorl, but 

at each horizon Krynine tested there is some indigo tourmaline; 

both varieties are always angular fragments of larger crystals. Outside the sedimentary rocks, schorl is found in the Bolton schist, but 

blue, pink, green, and colorless tourmalines are found only in pegmatites. In Krynine's samples of the Triassic sedimentary rocks 

the colored tourmalines are accompanied by pebbles of perthite and 

massive "vein quartz." The present writer believes therefore, that 

the Triassic rocks record the erosion of former pegmatites in higher 

horizons of metasediments east of the Triassic boundary fault.

DOLERITE

One large dolerite dike crops out 2.3 miles northeastward from 

Higganum, Conn. Northeast from the outcrops shown on plate 

56, dolerite float is found at several localities, and it is not improbable 

that the dike may continue beneath the glacial deposits. A roadcut 

at Higganum shows the dike to be 125 feet thick and to dip 50°-55° 

W. On several hillsides north of the Connecticut River, the dolerite 

has a chilled basaltic selvage against the Monson gneiss. The 

mineral composition of the dike is approximately 60 percent of 

labradorite, 35 percent of pigeonite and augite, and 5 percent of 

magnetite and ilmenite. The texture is subophitic; the fabric, 

equigranular. The dolerite is Late Triassic or post-Triassic in age, 

because it cuts the Newark group to the southwest (Mikami and 

Digman, 1957, map).

PLEISTOCENE DEPOSITS

Surficial deposits in this area include alluvium, sand, and gravel. 

The sand and gravel are crossbedded glaciofluvial deposits containing 

grains and pebbles of sandstone of Triassic age, quartzite, Glastonbury 

granite gneiss, graphic granite, pegmatitic feldspars, quartz, mica, and 

a small quantity of some dark minerals. The sands in this area are 

red to light buff, a coloration inherited from the rocks of the Newark 

group. The larger sand and gravel deposits form elongate areas 

paralleling major stream valleys. The largest deposits are found 

along Roaring Brook.

Flint (1933, p. 966-967) has described and classified the glacial
PEGMATITES OF THE MIDDUETOWN1 AREA, CONNECTICUT 639

deposits of the Connecticut River valley, and the stratified sand 

and gravel deposits in these two quadrangles are considered by 

him to be dominantly ice-contact fluvial deposits.

STRUCTURE

The structure of the Middletown area is that of a homocline in 

the north and a concordant domal structure in the south. North 

of Great Hill and Collins Hill, the westward-dipping homocline 

affects Bolton schist, mafic gneisses, and Glastonbury granite gneiss. 

It is not certain whether the Glastonbury granite gneiss and the 

Bolton schist are isoclinally folded or not. It is probable that the 

entire belt of Bolton schist east of the Glastonbury gneiss is overturned. At scattered locations within the Bolton schist, small drag 

folds indicate local overturning; so there must be considerable structural complexity that involves entire belts of rock. Locally overturned drag folds can be observed at the outcrops near U. S. Route 

6A toward Straits Hill (pi. 56).

South of Great Hill and Collins Hill, as far as the Connecticut 

River, there is an area of scanty outcrops showing divergent dips. 

An east-trending fault of indeterminate age probably offsets the 

metamorphic and igneous rock units in the area near Great Hill. A 

possible continuation of this fault has been mapped to the northeast 

(Herz, 1955).

At the south end of the area mapped (pi. 56), Monson gneiss shows 

parallel foliation within an orderly rock sequence. The domal 

structure of this sequence is clearly apparent.

The outcrops of mafic gneisses southeast of Folgelmarks Corners 

have oriented hornblende needles plunging 48° NW. and elongated 

feldspar stringers plunging 58° NW. In the vicinity of Collins Hillj 

drag folds and crenulations in the Bolton schist plunge 5°-25° N. 

The axes of rolls on the Strickland pegmatite were noted (Cameron 

and others, 1954, p. 335) to plunge 5°-25° N., but the keel of the 

pegmatite was found to be almost horizontal at the 125- to 140-foot 

levels. From these observations and from other northward plunges 

of drag folds within the Bolton schist, it is inferred that a low to 

moderate northerly plunge characterizes the fold axes (and the 

pegmatites) in the western part of the Middletown area.

The pegmatites commonly were emplaced parallel to strike of the 

schists, and less prevalently along the dip of the foliation as well. In 

areas where only pegmatites protrude from the overburden, the trend 

of their outcrops gives a fairly reliable indication of the strike of the 

country rock's foliation. The trend of the pegmatites changes 

from north-northeast to northeast as the strike of the foliation changes 

in the Glastonbury granite gneiss, Bolton schist, and mafic gneisses.
640 OOOSTTRIBUTIOINIS TO ECONOMIC GEOLOGY

The Triassic boundary fault also turns and trends in the same direction 

(pi. 56). The presence of a Triassic or pre-Triassic joint set is shown 

by the prominent dolerite dike that cuts sharply across both pegmatites and country rocks in East Hampton.

PEGMATITES

The Middletown area contains over 400 pegmatites, about 300 of 

which occur hi the Bolton schist, 75 in the Glastonbury granite 

gneiss, and 50 in the mafic gneisses. Additional pegmatities exist in 

the unmapped area farther south. Two types of pegmatites have 

been distinguished on the map (pi. 56): those in which potassium 

feldspar (with minor albite) is the most abundant mineral, and those 

in which sodium feldspar is the most abundant. The significance of 

this grouping will be considered later.

Pegmatites form a large percentage of the outcrops because they are 

the most resistant rocks hi the Middletown area. Topographically, 

the pegmatites are highs, usually forming breadloaf-shaped outcrops. 

They are most abundant in the schistose rocks, where the largest 

pegmatites also occur.

The pegmatites range in thickness from an inch or so to several 

hundred feet and in length from a few feet to several thousand feet. 

They are composed predominantly of microperthite, quartz, plagioclase, and muscovite. Beryl and tourmaline are widespread accessory 

minerals but usually total only a small fraction of 1 percent. In only 

one prospect, pegmatite 386 (pi. 56), does the beryl approach 1 

percent of the volume of the pegmatite. Biotite occurs in about 5 

percent of the pegmatite bodies, in quantities less than 0.5 percent, 

and shows both pseudohexagonal and rectangular bladed forms. 

Megascopically, the black tourmaline hi the pegmatites appears to 

be the same as that in the mica schist wall rocks, but under the 

microscope the tourmaline hi the schist is found to have the common 

pleochroism of brown to colorless, whereas the black tourmaline in the 

pegmatites invariably shows strong slate-blue to colorless pleochroism, 

indicating an alkali-rich tourmaline.

More than half of the pegmatites in the schistose country rocks 

formed sills that trend parallel to the enclosing schists. For this 

reason it is desirable to record the long directions of the pegmatite 

outcrops as a clue to the concealed wall-rock structure. In the 

Glastonbury granite gneiss, crosscutting pegmatites are more abundant, generally have random attitudes, and are mostly less than 10 

feet thick. North of South Glastonbury village, crosscutting pegmatites commonly strike northeast and are of greater size than those 

in the schist. Few pegmatites occur in either the massive Maromas 

granite gneiss or the Monson gneiss.
PEQMATITES' OF THE MlDDdJETOWlSP AREA, CONNECTICUT 641

DISTRIBUTION SIZE, SHAPE, AND MINERALS

About 75 percent of the pegmatites are in the Bolton schist and 

most of the other 25 percent are in schistose parts of the mafic gneisses. 

The distribution of pegmatites seems to have been controlled by the 

fissility of the invaded formations. The parallelism of many pegmatites and the Triassic normal faults indicates preferred directions 

of shearing, probably ancient faults cutting Precambrian basement 

rocks.

Some pegmatites in the Middletdwn area are less than 5 feet across 

and so small that they could not be mapped to scale, whereas others 

are 400 feet across and over 2,000 feet long. The small pegmatites 

are commonly tabular bodies; the larger pegmatites are less regular 

in form. The largest pegmatites lie between White Rocks and the 

Bear Hill area in Middletown. The relative abundance of potassium 

and sodium feldspar-rich pegmatites is not related to the formation, 

in which the pegmatite occurs but rather shows a regional pattern in 

which the potassium feldspar-rich pegmatites are more numerous to 

the south (pi. 56).

The areal distribution of beryl-bearing pegmatites shows no 

significant relation to any particular type of country rock. The even 

distribution of the beryl-bearing pegmatites probably indicates that 

beryl is an almost ubiquitous accessory mineral but was not found in 

many pegmatites because of the poor exposures. The color of beryl, 

likewise, bears no simple relation to the country rock intruded; beryl 

of all colors is found in pegmatites in any formation that has been 

deeply quarried.

TERMINOLOGY USED IN DESCRIBING PEGMATITES

Throughout this report the mineralogical composition of the 

granitic pegmatites, or pegmatite units, is indicated by naming the 

essential minerals in order of decreasing abundance. For example, 

"plagioclase-quartz-perthite pegmatite" indicates a rock in which the 

essential minerals are plagioclase, quartz, and perthite, each exceeding 

5 percent, and plagioclase is the dominant mineral (Cameron and 

others, 1949, p. 21).

The highly variable texture and coarse grain size of many pegmatites 

requires that the textural terms in common usage for other rocks be 

redefined for use in pegmatite studies. The grain sizes of country 

rocks have been given the customary designation of "fine," "medium," 

or "coarse," in accordance with common usage. 1 The grain sizes of 

pegmatite minerals are commonly many times larger than those of

i Coarse grained, above 1 mm in diameter; medium grained, between 1 and 0.5 mm; fine grained, less than 

0.6 mm.

461639 58 5
642 CONTRIBUTIONS TO .ECONOMIC GEOLOGY

igneous and metamorphic rocks; therefore, these textural terms, when 

qualified by the term "pegmatitic," are classified as follows:

Pegmatitic texture Grain size 

Fine grained__________________________ <Cl inch in longest dimension

Medium grained_____________________ 1-4 inches

Coarse grained_______--_______________ 4-12 inches

Very coarse_______________________..___ >12 inches

The normal texture of many pegmatites is more nearly that of a 

porphyritic than an equigranular rock and, therfore, it is difficult to 

determine average grain sizes. The limits given above have been 

applied to entire pegmatite units to indicate the size range that would 

be most frequently handled by quarrymen. Thus, if 20 percent of a 

pegmatite unit has a grain size of 1 inch, and 80 percent of the 

pegmatite has a grain size of 12 inches, the average grain size would 

be about 10 inches, or "coarse grained."

The term "unit," "zone," "fracture filling," and "replacement body" 

are applied to pegmatites as used by Cameron and others (1949, 

p. 1-2): "the structural and lithologic units that differ in mineralogy, 

texture, or both have been designated as: (1) fracture fillings tabular 

units that fill fractures in previously consolidated pegmatite, (2) 

replacement bodies units formed primarily by replacement of preexisting pegmatite, and (3) zones successive shells, complete or 

incomplete, around an innermost unit or core that reflect to varying 

degrees the shape and structure of the pegmatite body."

MINERALOGY

The pegmatites with more than 40 percent of potassium-bearing 

feldspar (microperthite) and those with more than 40 percent of 

sodium feldspar are separated on the map (pi. 56) on the basis of a 

visual estimate of the internal units of each pegmatite. The dominant feldspar in the pegmatites of the Middletown area is a microperthite, although the more general term "perthite" is used in this 

report for the purpose of brevity. The perthite is an intergrowth of 

microcline with a small amount of albite. The plagioclase-rich group 

(pi. 56) is not as abundant as the potassium-feldspar-rich group, but 

it contains more of the rare minerals.

Perthite forms the largest crystals in the pegmatites, and, even in 

pegmatites which average out to be fine grained, some perthite 

cleavage faces in the graphic granite may be more than 5 feet long. 

Exposure in the Strickland quarry are reported to have had perthite 

crystals more than 15 feet across. In the Hale quarry, cleavage faces 

average about 1 foot, and faces 5 and 10 feet across are common. The 

feldspar is cream colored with white albite lamellae barely visible to 

the eye. Some perthite always shows plaid twinning under the micro-
PEGMATITES OF THE MIDMJETOW^ AREA, CONN1EICTHCTUT 643

scope, although no plaid twinning was seen megascopically. The albite 

content of the microcline-microperthite is about 10-15 percent.

Large perthite crystals containing quartz lineaments are common. 

These intergrowths show the classic runic or cuneiform structures of 

graphic granite to a varying degree. It is noteworthy that the quartz 

lineaments lie in different directions at different places within a given 

perthite crystal, without any apparent relation to cleavage directions 

of the feldspar crystal.

The plagioclase is albite in all samples tested, and its composition 

ranges from An0 to An7 (table 6) .2 In many perthite-bearing pegmatites, albite makes up almost as much as the pegmatite as does potassium feldspar. In general, albite forms crystals less than 2 inches 

across, even in pegmatites where the perthite is much coarser grained. 

The albite crystals are whiter than the cream-colored perthite. Visual 

estimates of their relative proportions were made on the basis of this 

color contrast, as well as the presence or absence of albite twinning. 

The identifications have been checked by oil immersion methods. 

Determination of the refractive indices is often necessary to identify 

the feldspar. In most parts of pegmatites with aplitoid textures 

albite is the sole feldspar, but part of the aplitoid tourmaline-bearing 

unit in pegmatite 93 (on the west wall of Hale quarry) is perthite-rich.

The cleavelandite varietj^ of albite is quite rare. Notable occurrences are in pegmatites 117, 380, and the Gillette quarry. In pegmatite 380 at the Anderson No. 1 quarry, cleavelandite occurs intergrown with quartz and lepidolite in the innermost units of the pegmatite. The blades of cleavelandite are 2-4 inches long and contain 

less than 2 percent anorthite.

Lepidolite and spodumene are the principal lithium-bearing minerals. The lepidolite in pegmatite 380 is in flaky intergrowths with a 

grain size about 0.2 inch; it is bright pink, whereas minor occurrences 

of lepidolite in other pegmatites, as in pegmatite 165, are pale grayish 

pink.

TABLE 6. Index of refraction of albite, Middletown area, Connecticut

Pegmatite

93 ..........

65.............

60.............

12.............

387............

45.............

89 ..........

99 ..........

Quarry name

Hale. .............

HoweNo. 4 .......

Pegmatite unit of sample

Fine-grained quartz-albite ________________

Quartz-alblte-mlca. . ......................................

Quartz-albite... ...........................................

a±0.002

1.631

1.530

1.530

1.530

1.529

1.530

1.530

1.531

8 The anorthite content was determined In this range both by determination of refractive indices of grains 

of feldspar and by extinction angles measured in thin section. The anorthite content was found to be Am 

to An? by use of the unpublished feldspar chart compiled by Professor A dolph Knopf of Yale University.
644 COflSTTMBUTI'OiNlS TO ETONOMIC GEOLOGY

Chemical analyses of feldspars are listed in table 7. The feldspar 

at Howe quarry (pegmatite 73) with 2.32 percent of Na20 is believed 

to be a microcline sample; the feldspars from Strickland quarry (pegmatite 117) and pegmatite 168, with 3.04 and 3.12 percent of Na2O, 

are believed to represent perthite samples.

Quartz occurs interstitial to the feldspars as the principal mineral 

in several pegmatite cores, and as the principal or only mineral in 

tabular fracture fillings. The core in part of the pegmatite in the 

Gillette quarry is about 85 percent quartz, in crystals as much as 

4 feet across, through a maximum thickness of 35 feet. Tabular 

quartz fracture fillings in pegmatite 118 on Collins Hill are 3-12 

inches thick, nearly parallel, and cut across the outcrop at intervals 

of a few feet. The fracture fillings extend outward only to the margin 

of the pegmatite. External crystal faces of quartz are nowhere exposed except in a few vugs in gem-bearing pegmatites such as those 

in the Gillette quarry.

Muscovite is the most abundant accessory mineral; it is a major 

constituent of some pegmatite units. The usual habit is in pseudohexagonal books, from about 2 to 16 inches in diameter, and commonly with inclusions of tourmaline, garnet, and other iron-bearing 

minerals. The size of the inclusions ranges from less than 0.01 of an 

inch to 1 inch in diameter. Ruling, A-structure, wedged books, tied 

sheets, and air .staining may all be present in the micas of pegmatites 

in the Middletown area.

Biotite occurs in less than 20 percent of the pegmatites, but in 

some of these it amounts to a considerable proportion of the total 

mica. Two habits are common: pseudohexagonal books 1-4 inches 

in diameter, and ragged, bladed forms 0.5-12 inches wide and of 

lesser thickness. The books of biotite seem to be primary forms, like 

those of muscovite; but the blades of biotite give the appearance 

of being monomineralic fracture fillings.

Garnet is the most ubiquitous of the accessory minerals. Salmon, 

pink, or red garnets are present as idiomorphic crystals 0.05-0.1 inch 

in diameter in almost every pegmatite. Somewhat flattened garnets, 

as much as 0.8 inch in diameter, are found in a few places included in 

mica books.

Black tourmaline, called schorl, occurs in most pegmatites in Connecticut, and in thin section has a vivid indigo pleochroism. The 

size of the crystals ranges from microscopic to 6 inches in diameter 

and to a maximum length of 2 or 3 feet. The black tourmaline is 

most abundant in quartz, and striking subgraphic to graphic intergrowths of quartz and black tourmaline have been noted. Green 

and pink tourmalines occur in several pegmatites and, like the black 

tourmalines, these form idiomorphic crystals. Colored tourmalines-
TABLE 7. Chemical analyses and norms (in percent) of feldspar

[All samples represent commercial feldspar except the Haddam, Conn., oligoclase, which was associa

near contact with an unidentified pegmatit

Pegmatite 93 » Unidentified 

pegmatite 2

Oligoclase * 

Analyses

SiOj........... .............. ...............................

AljOa- -- .............. ...............

FezOs . .... ...

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

CaO... .. 

Na8O _______ . ____ . ____ .. ____ .... ______ .

K2 0.................................... ....................

HjO . ......... ........ .......... ........ ...............

71.00

8 16. 31

.22

3.44

8.66

.12

99.75

66.06

21.57

is

(?)

1.80

9.57

1.01

100.19 

2.633

64.26

21.90

(?)

2.16

9.99

.50

.29

99.00

Q....... . .. ...... ......................

ab.... .. . _ 

an.j ___ . ________ _________________

18

63

35

2

Norms

2

96

2

3

86

11

i Pegmatite 93: North end Hale quarry, Portland. Graphic granite. Specimen 

was ". . . varying in coarseness but all extremely fine grained. The quartz layers in 

this specimen average not more than 0.02 of an inch across and the feldspar layers not 

more than 0.05:inch across. Some small areas of pure feldspar were associated with the 

graphic granite in" this specimen, so that the silica percentage shown in the analysis is 

lower than it would be for graphic granite alone of this fineness. The feldspars are white 

potash feldspar (microcline), intergrown with smaller amounts of soda feldspar (albite), 

containing a little lime." (Bastin, 1910, p. 14.) Weight percentages from Makinen, 

1917, p. 178-180. 

.»Unidentified pegmatite: Haddam, Conn. Albite. Specimen 1757, Brush Collection, Yale Univ

field and Sperry. 

3 Oligoclase: Had

aged from two an

Makinen, 1917, p. 

« Pegmatite 73: 

» Pegmatite 117: 

« Pegmatite 168: 

* Pegmatite 50 or 

s Includes trace o
646 COINTRIBTJTI'OINS TO GiEK)I/OGY

of gem quality have been found in cavities in the Gillete and Strickland 

quarries while those quarries were active.

Beryl was identified in 62 of the 323 pegmatites studied, or approximately 20 percent. There are few published statements that 

permit comparison of the proportion of beryl-bearing pegmatites 

here to that in other areas. One such comparison is afforded by 

JollinVs statement (1944) that beryl occurs in 228 of almost 500 

pegmatites he examined in the Yellowknife area of Canada; i. e., 

about 45 percent.

The beryl content of the pegmatites ranges from nearly zero to a 

maximum of 0.8 percent (pegmatite 386, Gotta Walden quarry). 

The beryl crystals are idiomorphic, although many crystals are skeletal and contain varying amounts of quartz and feldspar. Muscovite 

films have developed along fractures in some larger beryl crystals or 

along basal partings. The largest crystal (pegmatite 386) seen by the 

writer was 16 inches across, about 2 feet long, and was singly terminated. The beryl is chiefly blue, green, and aquamarine, although 

a rare golden-brown beryl is found at several quarries and small fragments of pink beryl (morganite) are noted at pegmatite 381. Palegreenish-yellow to white beryl occurs at some localities; for example, 

pegmatites 165 and 164, both alone and with blue-green beryl; such 

beryl is difficult to evaluate quantitatively. The fine grains of beryl 

impregnating the schist adjacent to pegmatite 272 are pale yellowish 

to white; these are also the only anhedral beryl noted. Yellowishgreen beryl is also found in the schist adjacent to pegmatite 386, 

but there the crystals are well formed and as much as 4 inches across. 

The refractive index a and the BeO content of 18 representative beryl 

samples are given in table 8.

TABLE 8. Index of refraction of beryl, Middletown area, Connecticut

Pegmatite

93.. 

69.. 

109--. 

110-... 

116.- 

83.. .

73.. 

50.. 

113-- .

100.- 

20.. 

45-. 

Name

Hale......... ...

Case No. 2 ..........

Case No. 3. ... ...

Pelton..-. __ ..

Pratt....... ...

Unit

(?) .. 

pod.

 ..do.. 

mica (unzoned?).

N.±0.002

1,578 f i uRn

\ 1, 582

( 1. 5S2 

1,584

1,583

1,580

1,587

1,578

f 1,582

< 1, 582

I 1, 586 

f 1, 579

1 1, 582 

1,581

1,581

1,581

1,582

Color

Light green. .

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

.....do ... 

Greenish blue..

__ .do _ . -

..-.do.. -. 

BoO percent i

13.2

13.0

12.9

12.9 

12.6

12.8

13.0

12.3

12.9

12.9

12.4 

12.1

12.9 

12.5

12.5

12.5

12.9

1 The BeO content is derived from the refractive index by use of an unpublished chart showing variation 

of BeO.content with index of refraction by W. T. Schaller, U. S. GeologicaLSiir.vey. *
PEGMATITES OF THE MIDDUETOWJSP AREA, COJXTNiEICTtt!CTJT 647

Columbite (Fe, Mn) (Nb, Ta) 206 , was first identified near New 

London, Conn., in 1802. It was identified in the nineteenth century 

from pegmatites in the Middletown area: Haddam, Portland, and 

Middletown (Palache, Herman, and Frondel, 1944, p. 785 and 787). 

Two analyses of columbite believed to have come from one of the 

niobium-bearing pegmatites in the Middletown area are given by 

Wells (1937, p. 113-114). Columbite-tantalite occurs in a few 

pegmatites in this area, but only in mineral specimen quantities.

INTERNAL STRUCTURES

Many pegmatites in central Connecticut are nearly homogeneous 

bodies composed of perthite, quartz, and albite, with accessory muscovite, black tourmaline, garnet, and beryl. Most are finer-grained 

for a 1- to 6-inch thickness at the contact with the country rocks. 

This fine-grained selvage is the border zone described by Cameron' 

and others (1945, p. 373). It outlines the shape of the pegmatite, 

wrapping around a central core of coarser-grained pegmatite minerals. 

Pegmatites that are otherwise unzoned and have a more or less homogeneous fine- to medium-grained central unit rarely have been utilized 

commercially. Pegmatite 7. however, has a central unit of this type 

composed predominantly of feldspar with desirable ceramic properties; therefore, almost the entire pegmatite was utilized. Pegmatites 

in which an intergrowth of potassium feldspar with lesser quantities 

of quartz extends almost to the walls seldom are commercial sources 

of mica or rare-element minerals.

Although more than half of the pegmatites mapped are essentially 

homogeneous bodies, those that are characterized by two or more 

distinct lithologic, textural, or structural units make up the bulk of the 

bodies exploited for industrial pegmatite minerals. Bastin (1910, p. 

44) first recognized internal mineralogic units that parallel the trend 

of the pegmatite in his description of pegmatite 80 (the Wiarda 

quarry), in 1910. During World War II, the Geological Survey 

(Cameron and others, 1954) made detailed planetable maps of many 

of the exploitable pegmatites showing the internal zoning. In some, 

the internal structure is not distinct; in others, it is well defined. 

Most of the pegmatites of the Middletown area have not been opened 

up by mining, so the internal zoning may not be visible in the outcrop. 

Pegmatite units differ from each other in texture or mineral composition. Textural changes between units are frequently found, but for 

the most part the units are characterized by changes in the relative 

proportions of perthite and albite a distinction difficult to make with 

accuracy during mapping. Units that have boundaries paralleling 

the contact of pegmatite with country rock are called zones. Four 

types of zones have been recognized and have been designated in
648 OOiNTRIBUTIOCNlS TO ECONOMIC GEOLOGY

order from the walls inward as border zone, wall zone, intermediate 

zone, and core. Crosscutting units within the pegmatite are called 

fracture fillings or replacement bodies, depending on their origin.

Most pegmatites have a thin border zone in which plagioclase is 

either the predominant or the only feldspar. Wall zones may be made 

up of perthite and quartz, as in pegmatite 164, or perthite, quartz, and 

plagioclase, as in pegmatite 91 (Andrews quarry). A few pegmatites 

have intermediate zones, as in pegmatite 117 (Strickland quarry), 

where an intermediate zone 1 to 22 feet thick contains about 50 percent 

of perthite in a matrix of quartz and plagioclase. Pegmatite cores are 

characteristically massive quartz containing large crystals of blocky 

perthite, as in pegmatites 264 and 168. If the pegmatite pinches and 

swells, the core may be in discontinuous segments, as in State Forest 

No. 2 quarry. These core segments are 90 percent of quartz and 10 

percent of muscovite. In pegmatite 380 (Anderson No. 1 mine) a 

central unit is composed of more than 50 percent lepidolite, 35-45 

percent cleavelandite, and 5-10 percent of quartz.

Of 330 pegmatites mapped, 16 percent are zoned; and 84 percent are 

unzoned, except for a fine-grained border zone. Of 64 beryl-bearing 

pegmatites, 42 percent are zoned; of the pegmatites with less than 

40 percent of plagioclase, 21 percent are zoned; and of those with 

more than 40 percent of plagioclase, 10 percent are zoned. Many 

unquarried pegmatites now regarded as unzoned may have internal 

zones either concealed by overburden or not exposed at the top of the 

pegmatite.

The common assemblages of essential minerals of pegmatite zones 

in central Connecticut and elsewhere in New England constitute only 

5 of the 11 mineral assemblages noted (Cameron and others, 1949, 

p. 61) in the Black Hills of South Dakota. These five mineral assemblages, where present, occur in the following sequence: (1) plagipclase-quartz-muscovite, (2) plagioclase-quartz, (3) quartz-perthiteplagioclase, with or without muscovite and with or without biotite, 

(4) perthite-quartz, and (5) quartz. In addition to these 5 general 

assemblages, 2 others have been recognized in local instances: a plagioclase-quartz-spodumene unit in pegmatite 117 (Strickland quarry) 

may be an intermedite zone, and a lepidolite-plagioclase-quartz unit 

in pegmatite 380 (Anderson No. 1 quarry) may be a core. 

. Most fracture fillings in the pegmatites in the Middletown area are 

massive, milky to clear quartz; some are massive quartz con taming 

idiomorphic blocky perthite. Fracture fillings also carry accessory 

mica or beryl, as in pegmatite 16, where the quartz contains 0.2 percent of beryl. The mineral composition and the textures of fracture 

fillings in zoned pegmatites are often the same as those found in the
PEGMATTTEiS OF THE' MxDl>IJETO\^:'"iARElA," CO^NINIECTTOCTJT 649

inner zones, although fracture fillings are also known to cut unzoned 

pegmatites.

Replacement units, if present in the pegmatites of the Middletown 

area, are rare. Cameron and others (1954) have described a few such 

units in pegmatites at the Hollister and Strickland quarries.

RELATIONS TO WALL BOCK

The pegmatites in the Middletown area cut the Bolton schist, the 

mafic gneisses, the Glastonbury granite gneiss, and the Monson gneiss. 

Where contacts were observed, over half of the bodies were conformable to wall-rock structure. The relations of 323 pegmatites to the 

enclosing rocks are given in the table below.

Relation of pegmatites to enclosing rocks

Bolton schist. __-__---___-_____

Mafic gneiss _ _______________

Number of 

pegmatites

55

244

24

Concordant 

(percent)

45

49

50

Crosscutting 

(percent)

31

15

13

Structural 

relation 

uncertain 

(percent)

24

,.36

37

The ratio of concordant to crosscutting pegmatites is 1}£ to 1 in the 

Glastonbury gneiss but more than 3 to 1 in the Bolton and Middletown formations. The foliation in the latter two formations conforms 

for the most part to the shape of the pegmatite contacts, but the larger 

pegmatites in the Glastonbury gneiss (pegmatites 6 and 7) follow 

fractures that cut sharply across foliation

Many of the concordant pegmatites have deformed the enclosing 

schists, presumably by the intrusive force of the pegmatite-forming 

fluid. The schist at the pegmatite contact in the Gotta-Walden quarry 

is more contorted, richer in muscovite, and better foliated than at 

some distance from the contact. The discordant pegmatites in some 

places have deformed the schistose or gneissic foliation; an excellent 

illustration of this bending of the country rock was published by 

Bastin (1911, pi. 10).

Many pegmatites, like pegmatite 117 in the Strickland-Cramer 

mines (Cameron and others, 1954), have a close parallelism between 

their irregular contacts and the foliation of the enclosing schists. 

Others, like pegmatites 386 (Gotta-Walden) and 100 (Bordonaro), are 

in part; conformable and in part crosscutting (Boos, Maillot, and 

Mosier; 1949, figs. 5-14).

.The \pegmatites in the Glastonbury gneiss have mechanically deformed the foliation of the gneiss, but pegmatites in the quartz-mica
650 CKDOSfTRIBUTTOiNB TO ECONOMIC GEOIX>GY

schists of the Bolton schist have both deformed and altered their wall 

rock. Tourmaline occurs in the schist in some places for distances up 

to about 3 feet from the pegmatite, and is black megascopically. This 

metasomatic tourmaline (schorl) is grayish or brownish green under 

the microscope, in transmitted light, and is less strikingly pleochroic 

than tourmaline from the adjacent pegmatites.

Beryl crystals occur in the border zone in pegmatites 272 and 386 

and in the adjacent schist. In the hanging wall above pegmatite 272, 

the schist for an estimated distance of 6 inches contains muscovite 

(50-60 percent), beryl (20-24 percent), and garnet (15 percent).

A study of the regional zoning of pegmatites in relation to wall-rock 

formations would be of assistance in further prospecting for beryl or 

other minerals. Heinrich (1953, p. 74-75) observes that 10 of the 12 

beryl-bearing pegmatites mapped by Cameron and Shainin are in the 

Bolton schist or very near it. The present writer believes this is not 

a significant relation, since the quoted ratio of beryl-bearing pegmatites in the Bolton schist to those not within the Bolton schist (10 to 2) 

corresponds very closely to the ratio of pegmatites found in the 

Bolton schist to those found in the adjacent Glastonbury granite 

gneiss (244 to 55).

AGE OF THE PEGMATITES

The Middletown area probably contains more pegmatites on which 

absolute age determinations have been made than any other similar 

area in the world. In evaluating the reliability of these age determinations, Knopf (1948, p. 664 and 666; 1949, p. 4) used the following 

classification: (Only class I analyses are considered definitive; the 

others are less reliable.)

Class I analysis_______ U, Th, and Pb in minerals have been measured by

quantitative chemical analysis, and isotopic composition of lead has also been determined by mass 

spectrograph. This method admits calculated correction for nonradiogenic lead, as well as the disintegration of Th.

Class II analysis_______ U, Th, and Pb have been measured by quantitative

chemical analysis, and atomic weight of lead has 

been measured chemically. This permits allowance 

for disintegration of Th, but only an approximate 

allowance for nonradiogenic lead.

Class III analysis______ Quantitative analysis of U, Th, and Pb by standard

chemical methods.

Class IV analysis._______ Microchemical analysis of U, Th, and Pb.

Calculations of the age of the pegmatites hi central Connecticut 

have given successively younger ages, from the original 410 million 

years of Boltwood (p. 87) in 1905 to the present value of 260 million 

years (table 9). The latter is probably most nearly correct because
PEGMATITES OF THE MIDDUETOWN lARElA, CONDSTIECTICUT 651

allowance is made for the thorium present and the nonradiogenic lead 

(10-12 percent of the total lead), and more accurate determinations 

of the half-life periods were used.

This indicates an early to middle Carboniferous age, probably 

Mississippian. Class I determinations made on the neighboring 

pegmatite area at Bedford, N. Y., and at Branchville, Conn, (table 

10), give an early Paleozoic age, which indicates that the pegmatites 

of western and of central Connecticut (Middletown area), respectively, 

are related to different episodes of igneous activity. Lithium-bearing 

pegmatites are associated with both the Taconic and Acadian episodes 

of intrusion.

Age determinations by the strontium method are not yet dependable 

for minerals as young as those in central Connecticut. From Sr/Rb

TABLE 9. Age determinations of pegmatites by the lead method, Middletown, Conn.

Locality

Pegmatite 3, Spinelli prospect, Glastonbury. 

Pegmatite 01, Andrews 

quarry (formerly called 

Hale quarry), Portland. 

Pegmatite 91, Andrews

quarry, Portland. 

Pegmatite 117, Strickland 

quarry, Portland. 

Pegmatite 384 Rock Landing

quarry, Haddam.

Mineral analyzed and 

source of reference

Samarskite, Wells, 1

Nier.2 Baxter.' 

Uraninite, Foye and 

Lane.4

Monazite, Fenner ....

Uraninite, Foye and 

Lane.1

Class of 

analysis

I and II

III and IV 

III

IV 

IV

Latest calculation 

of age in millions 

of years to nearest 

10, and source of 

reference

260, Holmes 4 ......

280, Foye and 

Lane.'

300, Knopf ' ._.._

280, Foye and Lane.« 

280, Knopf '.......

Corresponding 

geplogic age

Early to middle

Carboniferous. 

Do.

Do.

Do. 

Do.

» Wells, R. C., 1937, p. 114-115.

» Nier, A. 0., 1941, p. 113.

' Baxter, Q. P., and others, 1937, p. 702-705.

* Holmes, Arthur, 1946, p. 134-137.

» Foye, W. Q.. and Lane, A. C., 1934, p. 127-138.

« Fenner, C. N., 1932, p. 327-333.

' Knopf, Adolph, oral communication, 1949.

8 Ingerson, Earl, 1938, p. 269-276.

TABLE 10. Age determinations of pegmatites from other localities of importance in

regional considerations ;

Locality

Bedford, N. Y.. .............

Branchville, Conn.. .........

Greenwich, Mass, (now

under Quabbin Reservoir).

Mineral analyzed and 

source of reference

Cyrtollte Muench. Nier." 

.Uraninite Boltwood 8 _.

Allanite Marble s .....

Class of 

analysis

I

III

IV

Latest calculation 

of age in millions 

of years to nearest 

10, and source of 

reference

350, Holmes >. _ ..

350, Knopf «.... .

400, Knopf ........

Corresponding 

geologic age'

Early Paleozoic

Ordovician(?). 

Do.

Ordovlclan(?).j

» Muench, 0. B., 1931, p. 350-357.

» Holmes, Arthur, 1946, p. 134-137.

» Boltwood, B. B., 1907, p. 253-267; 1905, pt. 2, p. 77-88.

* Knopf, Adolph, 1949, oral communication.

« Marble, J. P., 1949, p. 19-20.
652 OOlNTRIBUTIONIS TO ECONOMIC GEOLOGY

ratios in lepidolite, Ahrens (1949, p. 253, 255) calculated several 

unspecified pegmatites in the town of Haddam as being 270 million 

years old, several in Middletown as being 450 million years, and several 

in Portland as being 540 million years. Because any experimental 

error in the age of the pegmatites at Haddam is probably small and 

because 270 million years agrees with the lead age, Ahrens considers 

this to be the only satisfactory determination. He points out that 

where varying ages are obtained from analyses only the lowest age 

can be accepted, for the analyses made without determination of the 

isotopic constitution are subject to error in one direction because of 

the possible presence of primary, nonradiogenic strontium. The 

strontium method is not suitable for dating minerals less than 50-100 

million years in age, because of the slow rate of decay; it is best for 

dating Precambrian minerals.

The pegmatites of the Middletown area do not show a definite 

radial arrangement hi relation to, or exclusive association with, any 

specific rock unit, and therefore may be equally well related genetically 

to any of the igneous rock types. The foliated rocks, particularly 

the Bolton schist, contain pegmatites from the Middletown area to 

Long Island Sound, and it is apparent that these rocks have been the 

most favorable hosts for the pegmatites.

Cameron and others (1949, p. 6; 1953) have tentatively linked the 

pegmatites of central Connecticut with the Glastonbury granite gneiss 

(which they designate as Monson gneiss). The writer does not support this interpretation because a pegmatite in Massachusetts considered to be linked with the Monson gneiss has yielded a class IV 

radioactivity age determination of 370 million years (maximum value) 

(Marble, 1949, p. 19-20), whereas the pegmatites cutting the Glastonbury granite gneiss are 260 million years old.

There is little evidence to show that the fluids that formed the 

pegmatites of the Middletown area were derived from any particular 

igneous rock; in fact, it is conceivable that they were the product of 

differential anatexis. Whatever the origin of the liquids, they moved 

through the metamorphic rocks as a viscous fluid and crystallized 

in an orderly and systematic fashion that resulted in the formation 

of zones and other units.

The larger size and the greater proportion of perthite-dominant 

pegmatites in the southern part of the Middletown area suggest 

that the greatest intrusive activity and the highest temperatures 

during pegmatite emplacement occurred from White Rocks southward to the Killingworth dome. Because the pegmatites plunge 

mostly northward, the White Rocks-Killingworth dome area appears
PEGMATITES OF THE MLDDIJETOWN1 AREA, CONlSfiElCTICTJT 653

to represent an oblique section through the area that was the center 

of intrusive activity. Continued detailed mapping to the south might 

sbe expected to show an increase in the number of plagioclase-rich 

pegmatites.

The complex, highly irregular shapes of most of the pegmatites 

contrast strongly with the straight, tabular dolerite dike in East 

Hampton (pi. 56). The dolerite dike probably represents a relatively 

undifferentiated and fluid magma that came up along through-going 

fissures in cold rocks. The schists, on the other hand, appear to have 

been intruded by viscous pegmatite while more pliable and incompetent, and, therefore, presumably at a much higher temperature. 

The difference between the irregular form produced by pegmatite 

intrusion and the tabular form of dolerite dikes is probably produced 

by differing temperatures of the wall rocks at the time of intrusion.

The Maromas granite gneiss shows the same type of injection into 

schists at its margins as the pegmatites. The larger grain size of 

the pegmatites, compared with the Maromas granite gneiss, must be 

attributed to the greater concentration of certain components in the 

pegmatite liquid. The water content may have been slightly greater 

in the pegmatite fluids, but there is no clear-cut evidence of this.

In the past decades it was generally believed that the temperature 

range of pegmatites had been established within close limits. A 

review of certain laboratory experiments shows why there is less 

confidence today in stating the temperatures involved. One of the 

first experiments on the genetic temperatures of pegmatites utilized 

the inversion from "high" to "low" quartz (Wright and Larson, 1909, 

p. 438). "High" quartz was believed distinguishable, even in the 

massive mineral, by etch figures on the basal pinacoid. Thus, tests 

by Bastin (1911, p. 39) showed that quartz in the graphic granite 

from Hale quarry (pegmatite 93, referred to by Bastin as the Andrews 

quarry) showed characteristics of "high" quartz, and it was concluded 

that the pegmatite had crystallized at a temperature above 573 °C. 

The reliability of such tests was not accepted by Mugge (1907; 1932), 

who had first suggested that quartz might be used as a geologic 

thermometer.

In 1947, Ingerson (p. 375-379) tried experimentally to reproduce 

the genetic temperatures of pegmatites. By using data on the specific 

volume of water at high pressures and temperatures, Ingerson brought 

up to date the Sorby method of using liquid inclusions to yield calculated genetic temperatures of minerals containing such inclusions. 

Observing disappearance of the vapor phase at 153°-165°C, Ingerson 

applied calculated corrections and obtained the startlingly low temperatures of 155°-157°C as the genetic temperatures for two Connecticut pegmatitic quartz masses. These determinations were made
654 OONTRIBUTTOINIS TO ECONOMIC GEOLOGY

on specimens submitted by E. N. Cameron from two zones in pegmatite 109, exposed in the Case No. 2 quarry. The most probable 

temperature of origin for a beryl crystal obtained from the same 

locality was 175°C. All liquid inclusions were assumed to be primary 

ones.

In 1950 and 1951, Cameron, Rowe, and Weis (1951, p. 906-910) 

attempted to duplicate Ingerson's experimental results but found the 

vapor phase to disappear from 199° to 343°C rather than from 153° 

to 165°C. The reason for this disparity is not understood. Only 

fluid inclusions shaped as negative crystals in quartz or beryl, or 

tubular inclusions with long axes parallel to the c-axis of enclosing 

beryl crystals, were accepted as primary in the studies of Cameron, 

Rowe, and Weis (1951, p. 910), and the fluid inclusions in the Case 

quarry samples used by Ingerson were suspected of being secondary. 

Neither the current theory of origin for liquid inclusions nor the 

common interpretation of their behavior when heated is based upon 

experimental behavior of inclusions in synthetic melts. Such experimentation is needed before observance of liquid inclusions can 

yield valid suggestions of genetic temperatures for pegmatites.

A second recent method for obtaining genetic temperatures is used 

by Tuttle (1949, p. 723-730) in determining the variation in inversion temperature of quartz. Tuttle states that "the inversion 

temperature of quartz believed to have grown at low temperature 

is higher than specimens believed to have grown at high temperatures." First tests showed pegmatite quartz from the Black Hills 

inverting at lower than standard inversion temperature, showing 

affinity to rhyolite quartz samples. The results of the fluid inclusions 

and those of the inversion experiments are regarded by the present 

writer as incompatible; the problem of genetic temperatures for 

pegmatites cannot be solved until additional data have been made 

available and the theories on which the determinations were based 

have been checked.

Still another method for experimental determination of genetic 

temperatures is the decrepitation method, based on the presence of 

liquid inclusions. Scott (1948) reported 165 °C temperature for one 

quartz specimen from the Case No. 2 quarry (pegmatite 109); this 

result could not be reproduced by Cameron, Rowe, and Weis (1951), 

and it now appears that decrepitation methods can be applied reliably 

to crystals which have grown on the walls of cavities or open veins, 

but not to pegmatites (Konta, 1951).

Study of the internal units of pegmatites gives indirect evidence 

that they started crystallizing at a relatively high temperature and 

passed through a rather wide temperature range during cooling. 

Fersman (1951, p. 53) infers from theoretical evidence that crystal-
PEGMATITES OF THE M1DDUETQWW AREA, CONOTCTIlCOT 655

lization of pegmatites takes place in a manner analogous to magmatic 

differentiation; that is, in steps, with partial resolution of earlier 

formed minerals from time to time. Cooling steps in a magmatic 

fluid are delimited by physical constants such as the transformation 

of "high" quartz to "low" quartz and the critical point of water. 

Fersman names the stages of magmatic consolidation as magmatic 

<900°-800°C), epimagmatic (800°-700°C), pegmatitic (700°-600°C), 

pegmatoide (600°-500°C), hypercritical (500°-400°C), hydrothermal 

(400°-50°C), and supergene (50°-0°C). Of these, the pegmatitic, 

pegmatoide, and supercritical stages are considered the normal 

temperature range of most pegmatite rock. Other geologists (Brb'gger, 

1894; Landes, 1925, 1928, 1933; Schaller, 1925, 1927, 1933) have 

stressed the importance of hydrothermal solutions replacing simple 

pegmatite rock to form the complex pegmatites.

Pegmatites of the Middletown area are characterized by primary 

intergrowths of fresh minerals. The absence of relict textures showing 

older pegmatite units including graphic granite, together with the 

absence of hydrous alteration products around feldspar and other 

crystals, suggests that the observed pegmatite minerals are primary. 

Naturally, progressive crystallization in steps changed the composition 

of the rest fluid, so that replacement of one mineral by another within 

the chamber is to be expected at the interface between solid and fluid. 

Pegmatite textures show such a replacement of many minerals by 

one another; this intergranular replacement in nearly closed systems 

should not be confused with metasomatic replacement of pegmatite 

bodies. Pegmatites in this area show the intergranular replacement 

of almost every mineral present by almost every other mineral present; 

this replacement is evidence for rapid changes in the pegmatite-forming 

fluids as one mineral after another crystallizes. Metasomatic origin 

is considered improbable, however, for any of the pegmatite units 

examined by the writer in the Middletown area.

Cameron and others (1949, p. 102-103) have shown that the general 

variation in composition of plagioclase in pegmatites is from more 

calcic at the exterior of the body to more sodic in the center. This is 

in accord with what would be expected from a continuous reaction 

series in a closed system but would not be compatible with a replacement origin by hydrothermal solutions. Many minerals increase in 

size inward from the walls; for example, wedge mica books and tapered 

beryl crystals in pegmatites 108 and 109 (Case prospects). This 

implies a systematic process of crystallization in which the constituents of the minerals were furnished from the center of the pegmatite. 

Because many pegmatites show these tapered crystals in units that 

completely surround core units, it is difficult to understand how they 

could have grown in an open system such as is necessary for meta-
656 CONTRIBUTIONS TO ECONOMIC GEOLOGY

somatic replacement. In addition to the increased size of single 

crystals from the outer to the inner part of a pegmatite, there is 

generally an increase in grain size of all minerals toward the center.

Banded and mammillary structures like those shown in plate 57, 

at pegmatite 93 (Hale quarry) occur in less striking form in numerous 

other pegmatites, including pegmatite 95 (Wannerstrom quarry) in 

the Middletown area, pegmatites at Pala, Calif. (Schaller, 1925; 

Jahns, 1948, p. 7), pegmatites in Gunnison County, Colo., the Suzanna 

No. 5 and other pegmatites in Eight Mile Park, Fremont County, 

Colo. (Heinrich, 1948, fig. 11, p. 448), and others. These structures 

have been considered to be of replacement origin by some observers, 

whereas others consider the banding to be the result of flowage during 

crystallization. That such structures can have a deformational origin 

is illustrated by published photographs of siltstones and shales showing 

similar structures as the result of flowage (Rich, 1950, p. 725, 729, 

730, 734). The banded and spheroidal structures in the pegmatites 

near Middletown are interpreted as flow structures produced during 

the cooling of viscous pegmatite magma.

Fracture fillings similar to those of quartz perthite exposed in the 

Hale quarry cut the outer parts of a large number of pegmatites in 

this area. In no pegmatite has the writer traced the fracture fillings 

into the core, but the structural and mineralogic similarity of fracturefilling units to cores or zones observed in other pegmatites leads the 

writer to consider the quartz-perthite bodies as offshoots of the lastconsolidated part of the pegmatite. It is believed that in fracture 

fillings in. most pegmatites, the relations are similar to those shown in 

the so-called Hardesty Homestead pegmatite in South Dakota 

(Cameron and others, 1949, fig. 43) where the fracture-filling bodies 

are a part of the core.

Fracture fillings are believed to have been localized in tensional 

breaks during cooling of the outer part of the pegmatite, while the 

central part was still fluid. In some poorly differentiated pegmatites 

the fracture fillings in the outer units may have robbed the pegmatite 

of material that otherwise would have formed a core. Hydro thermal 

alteration has not been observed around any fracture filling in this 

area, and it is believed that the filling of fractures took place under 

the same conditions that interstitial quartz formed in granite.

The deformation of the wall rocks adjacent to some pegmatites is 

related to the pegmatite origin. At pegmatite 117 (Strickland quarry),, 

foliation planes of the surrounding schist parallel the bulges and 

depressions of the irregular pipelike pegmatite (Cameron and others, 

1949, fig. 29, p. 38). In others, such as pegmatite 100 (Bordonaro 

prospect), the thinner parts of the pegmatite are concordant, and the 

thicker parts are discordant to the wall rock. The deformation of
PEGMATITES OF .THE MIDMJETOWN lARE'A, CONINIEICJTICrDT 657

these wall rocks, together with the absence of relict .structures in the 

discordant parts of the pegmatite^ indicates that the pegmatitic fluid 

was forcefully injected.

The only replacement phenomena near the pegmatites are tourmalinization and an increase of the muscovite content of the schist near 

the contacts. The formation of these minerals in the schist depends 

on the addition of potassium, aluminum, boron, and water by the 

pegmatite. This is only a minor border phase of the emplacement 

process of the pegmatites. Because transfer by fluids is much more 

rapid than diffusion of ions through a solid, it is probable that pneumatolitic or hydrothermal solutions were involved in this wall-rock 

alteration.

In summary, the preponderance of evidence favors the formation 

of pegmatites from a magmalike fluid by a process of fractional 

crystallization. During some stages it appears probable that minor 

quantities of fluids escaped to alter slightly the surrounding wall rocks.

DESCRIPTIONS OP INDIVIDUAL DEPOSITS

More than 330 pegmatites were mapped and studied during the 

investigation of the Middletown area. Because the main purpose of 

the project was economic an evaluation of beryllium resources 

particular attention was given to estimating the mineral composition, 

internal structure, and grain size of the observed pegmatites. Studies 

were also made of unusual concentrations of industrial pegmatite 

minerals. Several pegmatites of special interest, either for their 

contained beryllium or other pegmatite commodities or for their 

geologic importance, are described in detail.

TTAT/TC QUARRY, PORTLAND PEGMATITE 93

Mine workings. The present Hale quarry in Portland was opened 

in May 1902, on land owned by the Hale family. The site was leased 

and operated by Harry Andrews of Glastonbury, who ground the 

feldspar at his mill on Hale Creek, several hundred yards from the 

quarry. The feldspar was sold after grinding to the Bon Ami Co. 

After the Andrews mill burned in 1906, the feldspar was sold to the 

Eureka Flint and Spar Co. The quarry was closed because of high 

labor costs during World War I. In 1916 the workings extended 

about 25 yards inside the present quarry entrance. The quarry was 

reopened in 1938 under a lease from the Hale brothers by the Eureka 

Mica Mining and Milling Co., of Portland, the producing subsidiary 

of the Eureka Flint and Spar Co., of Trenton, N. J. The quarry has 

been operated continuously since 1938, and approximately 100,000 

tons of feldspar has been shipped since that time.

.Present quarry operations, (J. C. Wilkes, president, Eureka Mica
658 OOINTRIBUTIOINS TO EtSOOSFOMIC GEIOI/OGY

Mining and Milling Co., written communication, 1948), begin on a 

bench 25 feet below the level of the quarry floor shown on plate 57. 

Dump material is being used to raise the top level of the two main 

dumps, rather than extend them laterally. The Hale quarry is one 

of the few operating feldspar quarries in Connecticut because of the 

large quantities of feldspar that can be produced with little hand 

cobbing. The hand-sorted feldspar is shipped 7 miles by truck to the 

Eureka feldspar mill, on the Airline Division of the New York, New 

Haven & Hartford railway, where it is ground to 200-mesh and shippeoV 

to potteries throughout the United States and to some foreign countries

The main opencut was 525 feet long and 45-100 feet deep in 1949, 

and an upper-level opencut is 130 feet long and 20 feet deep. The 

breast of the quarry is being worked southward along the eastern 

two-thirds of the pegmatite, avoiding the albite-rich tourmalinebearing rock in the west wall of the quarry (pi. 57). The quarry is 

being made self-draining. The quantity of feldspar sold from this 

quarry is, from 1902 to 1916, probably less than 10,000 short tons, 

from 1938 to 1949, about 100,000 tons. No salable byproducts 

have ever been obtained from this quarry. Operation of a picking 

belt as a means of removing waste from the feldspar was abandoned 

after a trial.

Geology. Pegmatite 93 (pi. 57) is zoned on the basis of essential 

minerals. The wall zone makes up the eastern three-quarters of the 

pegmatite; it is medium-grained perthite-quartz pegmatite, with subordinate albite and muscovite. On the western side a border zone of 

quartz-albite-mica pegmatite, from 0 to 45 feet thick, has striking 

mammillary structures (pi. 57) and bands of tourmaline-bearing rock. 

The mammillary structures contain bands rich in quartz, feldspar, 

and mica. Red bands are common and have been attributed to a 

high garnet content, but the color is almost entirely due to a surface 

discoloration of feldspar grains. The garnets present are very small 

and constitute less than 0.01 percent of the rock. Feldspar reserves 

are large because the pegmatite gives no sign of narrowing downward, and it extends at least another 350 feet south from the present 

quarry.

Beryl is not easily found. Small fracture fillings on the east side 

of the pegmatite contain up to 0.2 percent of visible beryl, and colorless beryl has been identified in thin sections of the fracture fillings. 

Apatite (fluorapatite) is distributed through the pegmatite in the 

Hale quarry and many others in the district. Although colorless, 

the apatite can be easily distinguished at night by its vivid, light 

orange fluorescence under ultraviolet light. The apatite crystals 

range in size from small specks to about 10 mm across. Fluorescent 

apatite is probably common in pegmatites; it has been recognized
PEGMATITES OF THE MIDDUETOWJSr lAREiA, COISHNIEICTHCTIT 659

in the so-called Harding pegmatite in New Mexico (J. W. Adams, 

oral communication, 1949). Postpegmatite fractures in the Hale 

quarry also display a bright fluorescence under ultraviolet light. This 

greenish-yellow fluorescence is emitted by a coating of hyalite which 

is invisible in daylight.

On the basis of contacts, now buried, between the Glastonbury 

granite gneiss and pegmatite 93 on the east side of the quarry, the 

pegmatite is believed to be crosscutting. It is probable that the pegmatite-forming fluids ascended along fractures in the Glastonbury 

granite gneiss and invaded the overlying Bolton schist. Emplacement was probably accomplished mostly by dilation of the wall rocks, 

but some assimilation took place. One partially digested xenolith 

was exposed in 1949 in the west wall of the upper-level quarry (pi. 57).

The mammillary flow structures in the pegmatite at the Hale quarry 

have fine-grained contact layers around them, indicating that some 

cooling of the surface took place where fresh pegmatite magma erupted 

into a cooling and consolidating crystal mesh.

HOWE NO. 1 QUARRY PEGMATITE 73

Mine workings. George Andrews opened the Howe No. 1 quarry 

about 1870. Several years later the northern half of the pegmatite 

was sold to Joshua and William P. Husband and the southern half 

was leased for 20 years to Charles Hall. Operations continued for 

some time in the northern half, although the southern half was found 

to contain better feldspar. In 1905 Louis W. Howe of South Glastonbury acquired both parts of the property and produced 65,000-70,000 

tons of feldspar between 1905 and 1928. The feldspar was recovered 

by hand cobbing, and the product was cobbed to contain as little 

sodium feldspar and quartz as practicable; fragments with visible 

muscovite, beryl, or tourmaline were put on the dumps. No byproducts were sold. The ratio of recovered feldspar to waste was about 

1:3. The present owner of the property is Consolidated Feldspar Co.

In 1949 the opencut was 100 feet wide, almost 800 feet long, and 

100 feet deep at the south end. The north end has 25 feet of backfill 

and the south end is full of water. Quarrying in the north end of the 

pit was abandoned in 1928, partly because ground water flowed into 

the opencut at the rate of about 300 gallons per minute, requiring the 

continuous operation of a 12-horsepower pump. The quarry employed 

30-60 men operating steam power drills and 15-25 men in the grinding 

mill. Most of the feldspar was ground to 60- or 80-mesh for use 

in manufacturing bathroom fixtures and porcelain insulators, and the 

remainder was ground to 200-mesh for use in scrubbing compounds. 

The largest amount of ground feldspar sold in any one year was 8,300 

tons in 1907, and the smallest amount was 3,000 tons in 1908. Until
660 OONTRIBUTIOINS TO ECONOMIC GEOLOGY

1915 the feldspar was taken in ox-drawn carts to the Connecticut 

River, ferried across to Rocky Hill, loaded onto 3,000-ton barges and 

carried by barge to the potteries in New Jersey. From 1915 to 1924 

the output was carried by trolley to the Ho we grinding mill. From 

1924 until 1928, haulage to the mill in Glastonbury was by trucks. 

Since 1928 the quarry has been idle.

Geology. Pegmatite 73 is exposed only as remnants on the walls of 

the Howe quarry. The body is concordant locally but, in general, 

dips more steeply than the enclosing Bolton schist so that it must be 

crosscutting at depth. The pegmatite consists of at least three units: 

a thin wall zone of plagioclase-perthite-quartz pegmatite that contains about 0.08 percent of beryl in crystals as much as a fifth of an 

inch hi cross section, a core of perthite-plagioclase-quartz pegmatite 

containing less than 1 percent of muscovite, and small fracture filling 

units about a foot hi maximum thickness that contain as much as 1 

percent of beryl. Other units may be present, but the lower workings 

of the quarry were flooded at the time of examination. The pegmatite narrows slightly from top to bottom of the pit.

The core of perthite-plagioclase-quartz rock appears to have 

formed most of the pegmatite and to have been coarsely crystallized 

and therefore amenable to hand cobbing of the quarried rock. Although the beryl content was extremely small, crystals more than 6 

inches in diameter have been described by former quarry workers. 

No rare minerals have been reported from this pegmatite. The large 

size of this pegmatite is its main distinguishing feature; its geologic 

history is typical of the numerous simple, granitic pegmatites intruded 

in the area during Mississippian(?) time.

SPINEULI PROSPECT PEGMATITE 3

The Spinelli prospect was first worked for feldspar in 1912. Since 

that time only a few pounds of mica and samarskite have been mined; 

the samarskite was used for lead-uranium age determinations (table 

9). The prospect is owned by Vito Spinelli, of Boston, Mass., and 

Bovo Pezzana, who lives near the property.

Geology. Cameron and others (1954) give a detailed description of 

the geology. Pegmatite 3 (fig. 60) is a lenticular dike exposed for at 

least 280 feet along the strike and having a maximum width of 30-40 

feet. This northeastward-trending dike is cut near the middle by a 

steeply dipping northwest-trending fault. The pegmatite intrudes 

Glastonbury granite gneiss and is made up chiefly of plagioclaseperthite-quartz pegmatite. Mica occurs as greenish, reeved, and 

fractured muscovite, the books are all less than 4 niches across and 

usable only as scrap mica. The samarskite occurs only in a small 

pod, 14 by 3 feet, near the western end of the pegmatite. The pod is a
PEGMATITES OF THE MIDDUETOWN (AREA, CONNECTJICUT 661

Medium-grained plagloclase* 

perthite-quartz pegmatite

EXPLANATION

Contact 

Between pegmatite unfa "mlt of

Medium-grained perthite-quartzmica pegmatite, bearing samarskite

Fault, showing dip Km of excavation 

Dashed where approximately ^ Wll>// 

Foot of dump /oca/<"/

tZT

Strike and dip of foliation

Glastonbury granite gneiss 

Microcrino-quartz-o/igocta$«-tiot/'t»

40-40 t

Contact, showing dip 

Dashed where approximately^ 

, located

Approximate.scale

Sketch map by V. E. Shainln, 1943 Revised by F. Stugard, August 1949 

FIQUEE 60. Spinelli pegmatite prospect, Qlastonbury, Hartford County, Conn.

medium-grained perthite-quartz-mica pegmatite; the richest area of 

9 by \% feet was found by Cameron to contain 0.3-0.4 percent samarskite. The largest pieces of samarskite have been removed, leaving 

only fragments 0.1-2 niches long. The perthitic feldspar around the 

samarskite is salmon red. Zonal structures have not been clearly 

exposed in the pegmatite at the Spinelli prospect. The size of the 

pegmatite is insufficient to support any sustained mining.

PAST PRODUCTION OF PEGMATITE MINERALS

The pegmatites of the Middletown area were mined intermittently 

for feldspar and mica from about 1825 to 1865 and continuously since 

then. The recorded production of crude feldspar is 416,216 long tons 

and of mica 4,131 short tons. The partial production records for 

pegmatite in Connecticut are given in tables 11 and 12. Probably 

90 percent of the Connecticut feldspar and nearly all the mica has 

come from the Middletown area. For those years in which Connecticut production of feldspar was reported jointly with that of New 

York, it may be assumed that the Middletown area produced a large 

part of the quantity reported, the remainder coming from the quarries 

at Bedford, N. Y. In table 11 a suitable notation has been made 

where the total production includes some material that came from 

States other than Connecticut.
TABLE 11. Connecticut feldspar productio

[Source: U. S. Geol. Survey, 1882-1931, U. S. Bur. M

Year

1883 

1884. 

1885 ____________ 

1886 ___ . _ .... _

1887-99.. - _ ......

1900.- - 

1901... ____ _ .. .

1902.. .. 

1903.... . .-.

1904 ___ . ........ .

1905. _ ..... .............

1906. _ .....

1907 __ ......... __ .. ...

1908.. . 

1909.. . 

1910.. ___ . _ . _ . .... .

1911. _____ . __ . .....

1912... 

1913. _ ... _ . ____ . ...

1914. ___ . _ . __ . .....

1916.... 

1916 ___ .. __ . _ ... ...

1917. ________ . .. .... .

1918..... 

1919 ____ . ___ . .......

1920... ___________ .

1921.... - ...

1922.. 

1923.... __ . .......

1924. . . 

1925-. 

1926 ___ . _ . ...........

1927 ___ - __ . .........

Number of 

operating 

quarries In 

Conn.

8

4

4

7

3

3

6

8

9

10

9

Crude feldspar (long 

tons except 

as noted)

6,000

6,000

4,500

7,500

11,584

i 3, 514

15,304

12,163

' 10, 501

122,554

1 10, 663

1 7, 775

19,633

i 9, 996

i 9, 118

i 9, 556

1 10, 166

111,099

i 2, 778

11, 012

10,455

5,305

9,715

7,719

9,565

7,499

8,780

6,572

10,426

11, 436

6,123

Value

$37,500

(at Trenton, N. J.)

6,800

4,902

23,561

6,274

47, 036

74, 036

15, 825

28,522

32, 903

27,450

34, 943

35, 867

42, 965

10, 715

49,554

43,160

29,419

84,050

64,006

65,864

47,887

75, 379

51,442

71,201

87, 844

43,319

Ground 

feldspar 

(short 

tons)

8,006

7,275

8,742

7,435

8,456

9,040

7,500

11,500

9,934

4,011

8,743

7,379

9,519

10, 122

5,414

10, 732

2,741

Value

$61, 500

49, 956

59,642

55,628

63,228

60,500

50,500

40,500

14, 491

57,071

46, 107

59, 154

79,903

40,326

62, 409

27, 425

34, 272

22, 708

49,063

61, 147

46,927

Name or n

3....... __ . _ ..

3..... . __ 

1. ...... _ .......

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

Louis W. Howe an
192S

1929.. ..................

1930-34. ________ . ...

1935.. ....................

1936. .....................

1937.. ....................

1938... ____ ... _ . .....

1939. ___________ ..

1940. .....................

1941. ___ . _ . _____ ..

1942......................

1943. _________ ... ...

1944. ___________ ..

1945. .....................

1946. ___ ....... .........

1947......................

Minimum totals for Connecticut.*

6,292

2,726

17, 103

7,461

10, 033

94 4A4

13, 693

19 8ft7

11, 618

11, 370

11,735

16, 555

15,408

416,216

4fi QQfi

21, 056

99, 770

45,153

128, 348

92,397

92,076

76,463

75, 394

74, 778

98,407

100, 152

2,525

139, 074

36,764

Co., Middletown; 

ganum.

1... _ . __ . ____

1... __________

1... _ ... ______

1 ___________

1 .... .... _____

1.. ...... _____ ..

2... __ . ___ . ___

1 Short tons.

8 Includes all specified Connecticut production.
TABLE 12. Mica sold or used by Connecticut producers 1985-47 

Yeari

1935--. 

1936-.. 

1937 __ . ______ . _____ .,.. __ - _

1941.. ______ . _ _ .

1942 __ ....... __ . _ . _____ 

1943... _ . _____ __ - -. -

1944. ________ .. ____ . _ .. ___ ..........

1945. _ 

Uncut punch mica

Pounds

169, 923 

156, 232 

311, 091 

157, 816 

196, 377 

- - 165, 186 

26, 219 

60,823

1, 243, 667

Value

$5, 943 

6,750 

12,242 

11, 135 

14, 321 

- 26, 528 

9,558 

3,246

$89, 723

Uncut mica larger than 

punch mica

Pounds

..95,327 

92, 952 

90,720 

95,009 

25, 106 

36,956 

50,857 

1,009

. 484,936

Value

$46, 817 

49, 900 

31,046 

118, 761 

16, 570 

38, 711 

137, 371 

6, 879

.$446,255.

Total u

Pound

265, 2

249, 

401, 

252, 

221,4

- 202,1

77, 0

61,8

1,731,6

i Productions for 1938-40 and 1946 not recorded; in 1947 no mines were producing mica.
PEGMATITES OF THE MlDM-ETOWfti AREA, COOSfiNlECTICtJT 665

Mica production records in Connecticut before 1935 are incomplete, 

although it is known that in 1904 Connecticut ranked eighth of nine 

producing States. In 1915, 300 pounds of sheet mica and 1 ton of 

scrap mica were mined, but not sold. .A small quantity of scrap mica 

was mined in 1924, and in 1929 mine-run mica was being sold from 

Strickland quarry by the Eureka Mica Mining and Milling Co. and sheet 

and scrap mica from the West Side mine, by the Huse-Liberty Mica 

Co. In 1932 Connecticut ranked third among the mica-producing 

states.

After 1935 the production was annually recorded in detail in the 

Minerals Yearbook (U. S. Bur. Mines) (table 12) and also by Cameron 

and others (19.54), who give a breakdown of the grades of mica 

produced in the Middletown area during World War II.

The quantity of mica produced in Connecticut has depended upon 

the current price rather than the amount available in pegmatites. 

The national average sales value of domestic uncut sheet mica during 

1942 (U. S. Bureau of Mines, 1,943) is given in the table 13. The 

maximum price for scrap mica sold from New England in 1945 

(U. S. Bureau of Mines, 1946) was $25 per ton f. o.'b.

Neither spodumene nor lepidolite has been produced commercially 

within the district. Several tons of beryl were marketed from the 

Strickland quarry, as a byproduct of pegmatite mining, after its 

reopening in. 1942. During this period several tons of spodumene 

were put on the dump. The Anderson No. 1 quarry (pi. 56) was 

worked during World War I for lepidolite, but none was sold.

TABLE 13. Average price of domestic uncut sheet mica during 194% 

(U. S. Bur. Mines,

Size In inches

1H x 2... _____________________________

2 x 2_ _ ____ _ _ ____ __________ _ __.

2 x 3_________, ________________________

3 x 3___-_-__---_______._______________

3x-4,__._.____________________,___-^__-

3x5________ _ ___. __ ______ __ _____

4 x 6__ __ __ _ _______________ _ _____

6 x 8___ ________________________ _ _

8 x 10_____________________________-__.

Price per pound

Clear

$1. 04 

1.61 

2. 44 

2. 98 

3.57 

4.18 

5.21 

7. 12 

. 13. 47

Stained or spotted

$0.88 

.51 

.77 

.92 

1. 20 

1.51 

1.69 

2.89 

4. 76
666 OONTRIBUTTOCNIS TO EOOOSPOMHC. GEOLOGY

BERYL

The beryl deposits of the Middletown area have been described by 

Cameron and Shainin (1947). . Of 120 pegmatites .examined by them, 

only 10 averaged more than 0.2 percent of beryl. The 10 highest 

grade pegmatites contain 0.4 percent of beryl, almost all of which is 

too small to be separated from the rock by hand, Beryl was found 

disseminated through pegmatites, mostly in small low-grade deposits. 

Border, wall, and intermediate zones were all found to contain beryl 

in some pegmatites; pods and fracture fillings also contain beryl in 

variable proportions ranging up to 1 percent and more of the unit, but 

these units are small.

The beryl resources in 10 pegmatites were determined by Cameron 

and Shainin on the basis of crystal counts and measurements on pegmatite exposures. The inferred resources of beryl totaled 859 tons 

in 208,000 tons of rock, an average content of 0.4 percent. Additional reserves were measured by the present writer in many other 

pegmatites, but the largest additional reserves were found by examination of pegmatite quarry dumps.

The beryl reserves of the Middletown area, Conn., are estimated by 

the writer to be 2,430 tons of beryl in 2,320,000 tons of rock. These 

deposits, containing an average of 0.1 percent of beryl, are mostly 

in scattered low-grade pegmatites and are therefore economically unfavorable. The part of the reserves that might practicably be utilized 

as mill feed for the recovery of beryllium are the mine dumps at the 

Hale, Louis W. Howe No. 1, and the Strickland-Cramer quarries. 

Spectrographic analysis of dump samples indicates that 570,000 tons 

of broken rock in these dumps contain about 880 tons of beryl.

It is believed that recovery of beryl from these low-grade (0.15 

percent beryl) mine dumps would be possible in a flotation-process 

separation plant. This might be practicable if strategic uses are 

found for beryllium, and if at the same time the major mineral constituents of the dumps were salable. Until that time recovery of 

beryl is likely only as a byproduct of the feldspar industry if that industry should undertake construction and operation of a flotationprocess mill nearby.

Since adequate search regularly discloses beryl in well-exposed 

pegmatites and since it is difficult to identify white or colorless beryl, 

it is probable that many poorly exposed pegmatites actually contain 

between 0.1 and 0.2 percent of beryl. The probable reserves, therefore, are about five times the reserves given above. Almost none of 

this beryl is recoverable by hand cobbing since much of it is less than 

0.1 inch in grain size.
PEGMATITES OF THE MIDDUETOWN AREIA, CONNECTICUT 667

The largest mine dumps in the Middletown area are in the idle 

Strickland-Oramer quarry and mine (pegmatite 117), the idle Howe 

quarry No. 1 (pegmatite 73), and the large, currently operative Hale 

quarry (pegmatite 93). In an effort to evaluate these dumps for 

beryl content, over 50 grab samples were taken from various parts of 

the dumps at each of these quarries. All grab samples were shoveled 

from about 2 feet below the weathered surface of the dump and 

were spaced by eye to include the various dumps at each quarry 

in amounts roughly proportional to their size. The samples for each 

quarry consisted of pegmatite fragments less than 2 inches across; 

these were reduced to about 10-mesh by use of jaw and gyratory 

crusher. The bulk samples were quartered to obtain the samples 

shown in table 15. These samples were quantitatively analyzed for 

BeO by spectrograph in the Geological Survey laboratories (table 14) 

after further reduction. Semiquantitative spectrographic analyses 

were made of other metals. The Spinelli prospect (pegmatite 3) dump 

was sampled by picking small fragments of pegmatite from the larger 

ones in the dump.

Because of the method of crushing, the iron content of the samples 

undoubtedly is several times the true iron content of the dumps. 

The 0.004 percent of beryllia content of the Spinelli prospect sample 

is the same order of magnitude expected if the beryllium be in solid

TABLE 14. Spectrographic analyses (in percent) of four pegmatite dump samples, 

Middletown area, Connecticut

["X" indicates an undetermined digit from 1 to 9. Looked for but not found: Co, La, Ce, Er, U, Ag, P, As, 

Sb, Qe, Tl, Cd, Ta, Mo, Zn. Analyst: Janet D. Fletcher, U. S. Geological Survey]

BeO.... ... . 

Ba. ..... 

8r . . ... ___ __ . .

Mn-. 

T1-.........-.. . ..

8n,.. . 

Or........................... ... .................

V. - 

Ni.. ....... ......... .......... 

Cu .......... ...... . . . . 

Pb ... 

Bl.... 

Zr .... 

Cb (Nb). ..... ..... ...... .. .. ...

Y. ............... .., . . 

B. ..................................................... Me-O

CaO.. -

NajO... ..... ...... 

Sample '

1

0.02 

.OX 

.OOX 

.OX 

.OX

.OOX 

.OOX

.ooox

.ooox 

.ooox

.OOX

.OOX

.ooox 

.ox

.1-.3 

1-3 

.1-.3

4-7

2

0.02 

.OOX 

.OOX 

.OX 

.OOX

.OOOX 

.OOX

.OOX 

.OOX 

.OOX

.OOX

.ooox

.OOX 

.OOX <1

.3 

.3- .6 

4

3

0.02 

.OX 

.OOX 

.OX 

.OX

.OOX 

.OOX

.ooox 

.ooox 

.ooox

.OOX

.OOX

.ooox 

.ox

.3-. 6 

.3 

.3-. 6 

4

4

0.004 

.OX 

.OX 

.OX 

.OX 

.OOX 

.OOOX 

.OOX

.ooox 

.ooox

.OOX

.OOX

.ox

.OOX 

.OOX 

.OOX <.l

.3-. 6 

.3-. 6 2-4

' Sample 1: Dump material, Strlckland-Cramer mine and quarry, Portland. Composite of 57 grab 

samples totaling 280 Ibs.

Sample 2: Dump material, pegmatite at Howe No. 1, Blastonbury. Composite of 50 grab samples totaling 

120 Ibs.

Sample 3: Dump material, Hale quarry, Portland. Composite of 77 grab samples totaling 170 Ibs.

Sample 4: Dump material, Spinelli prospect (samarsklte bearing). Grab sample weighing 40 Ibs. 
668 OOfNTRIBUTTOCNlS TO ECONOMIC GEOLOGY

solution in the feldspar. Spectrographic measurement of the Be 

content of perthite shows about 0.001 percent (J. D. Fletcher, written 

communication, 1949). The 0.04 percent of beryllia content of the 

three samples from large quarry dumps indicates a beryl content of 

between 0.1 and 0.2 percent.

The constancy of beryllia content in the three large pegmatite 

dumps is notable because in the Strickland-Cramer mines the beryl 

is believed by Cameron and others (1954) to be confined to one unit * 

the quartz-cleavelandite zone, whereas in the Ho we No. 1 and the 

Hale quarries the beryl is disseminated through the pegmatite. Thus, 

it appears that the pegmatite-forming solutions had a nearly constant 

beryllia content, regardless of the manner in which it was localized 

during crystallization.

This low-grade beryllium-bearing rock is the largest beryl resource 

in the area. Exploitation of the low-grade resources in this area will 

depend upon the development of an economical procedure for removing beryl from quartz, feldspars, tourmaline, and other pegmatite 

minerals and market conditions of the minerals recovered.

Flotation tests (Lamb, 1947; O'Meara, 1948) on 11 tons of representative pegmatite from the Gotta-Walden prospect (pegmatite 386) 

showed that from a minus 20-mesh sample containing 0.14 percent of 

BeO (about 1.3 percent of beryl) 69.3 percent of the beryllia could be 

recovered in a concentrate assaying 8.05 percent of BeO. Since appreciable quantities of pegmatite containing as much as 1 percent of 

beryl do not occur in this area, a successful flotation extraction must 

involve a process capable of recovering beryl from even lower grade 

material, probably as low as 0.15 percent of beryl. The percentage 

of recovery of the BeO must be expected to be somewhat lower than 

the test run by the Bureau of Mines on the higher grade beryl pegmatite.

It is clear that no beryllium ore exists in the Middletown area at 

present, if by ore is meant an aggregation of minerals from which 

beryllium could be extracted at a profit. However, if the quarried 

pegmatite already above ground were treated in a flotation plant for 

other minerals, such as feldspar, it might be possible at a low additional 

cost to install the cells necessary to recover a part of the beryl.

A comparison of several items in older chemical analyses, cited in 

table 15 (Wells, 1937, p. 24) from Howe No. 1 and the StricklandCramer mines, with comparable items in the spectrographic analyses 

of the dumps (table 15) shows a remarkable agreement between results 

of different samplings many years apart and between completely 

differing analytical methods.
PEGMATTTEiS OF THE MIDDLETOWN ARE'A, CONNECTICUT 669

TABLE 15. Pegmatite analyses (in percent) Middletown area, Connecticut 

[Analyst: R. 0. Wells; samples collected by F. J. Katz]

SiOj....--.. __....___..._-__. _

A12 03 -------------------

Fe2 03 (total Fe)__ ________

MgO 

CaO. _ -- -_--._-- -----

Na2 0 

K2 0___ _-___.._ _ _,--__--__-

H2 0 (total) __________ __.

TiOa-...-.. _ -- _-_---

Total ___________ __

Samples '

A

72.42 

15.88 

.54 

Trace 

.65 

3.74 

6.24 

.46 

.05

99.98

B

71.00 

16.06 

.63 

.02 

.32 

3.75 

7.65 

.34 

.04

99.81

C '

72.20 

13.81 

.86 

None 

.62 

4.05 

4.55 

.45 

.17

96.71

D

74.42 

15. 13 

.52 

None 

.44 

5.40 

3.49 

.39 

.02

99.81

> The exact locality of samples 0 and D Is unknown: they are given from Wells (1937, p. 24).

A. Howe quarry No. 1, Olastonbury, east wall. Sample Included feldspar, muscovite, and quartz.

B. Strickland quarry, Portland, across width of quarry.

C.' Eureka quarries, near Middle Haddam village, East Hampton.

D. Qildersleeve prospect, Portland.

FELDSPAR

Feldspars form one of the essential constituents of most pegmatites; 

consequently, feldspar of commercial quality occurs in many pegmatites. The size, shape, and structure of the perthite-bearing units 

determine whether or not feldspar with the desired characteristics can 

be mined profitably. Perthite occurs in larger crystals than the other 

feldspars and tends to form either a core or a hood-shaped zone above 

a core. Some of the largest feldspar quarries have operated entirely 

within the hood of a zoned pegmatite; others, such as the Hale, in 

a core. The large feldspar resources in the Middletown area so 

greatly exceed trade demand for feldspar within commercial haulage 

range that no tonnage computations were made.

MICA

Mica in homogeneous pegmatites is disseminated and usually small, 

Some wall and intermediate zones contain sheet mica, and most of 

the sheet and scrap mica production has come from these zones. 

Fracture-filling bodies and pods contain mica but seldom produce 

usable sheet mica.

In general, the Connecticut mica has many structural and mineralogical defects and therefore is classified as scrap mica; only an extremely small proportion can be used as sheet mica. Connecticut 

sheet mica is therefore not competitive with peace-time overseas 

sources of supply. Scrap mica comprised 1-3 percent of most Middletown area pegmatites.
670 CONTRIBimOlNIS TO ECONOMIC GEOLOGY

QUARTZ

No recorded production of quartz has come from the Middletown 

area. As an intergrowth with other minerals, quartz is one of the 

most abundant constituents of every pegmatite. Although not a 

practicable product for hand cobbing, quartz could be a byproduct of 

every froth-flotation feldspar separation. The tonnage reserves of 

quartz in this area are vast.

NONPEQMATITE MINERALS

Although the purpose of this report is the determination of certain 

pegmatite mineral resources of the Middletown area, nonpegmatite 

mineral resources observed during the fieldwork are briefly noted for 

the sake of completeness.

NICKEL AND COBALT

Nickel and cobalt were mined in the 18th and 19th centuries near 

the present Camp Jenkins, on the southeast slope of Great Hill 

(pi. 56), within what is now Meshomasic State Forest, East Hampton 

(formerly Chatham). The vertical and inclined shafts and the 

foundations of the mill can still be seen. No nickel or cobalt minerals 

are visible in the old workings, and no further production of metal is 

likely. About 20 tons of material, intended for use in China as smalt 

in the manufacture of chinaware, were shipped during early operations. 

An assay in the mid-19th century showed run-of-the-mine ore to 

contain 2.2 percent of metallic minerals, and it was believed at that 

time that ore separators of contemporary design could derive concentrates of 20 percent metallic mineral content, about equally nickel 

and cobalt minerals, together with some hydrous ferric arsenate, 

scorodite. The history of this old mine has been given by Blake 

(1882). Schairer (1931, p. 109) identified arsenopyrite, scorodite, 

niccolite, sphalerite, galena, and smaltite-chloanthite in the overgrown 

mine dumps. It is reported that five attempts to work this deposit 

failed financially between 1762 and 1855. Further interest must 

depend upon finding a larger quantity of the metallic minerals reported 

earlier or finding associated radioactive minerals.

Reports from the mine at Cobalt, Conn., attracted considerable 

early attention, first for cobalt and shortly thereafter as a possible 

source of nickel (Whitney, 1854, p. 496-497). A description of ores 

from this mine was published after the ores were exhibited at the 

New York Crystal Palace Exhibition of 1853-54 (Goodrich, 1854); 

ores from the surface to a depth of 3 fathoms included cobalt bloom, 

nickeliferous mispickel (arsenopyrite), and finely disseminated "smaltine" in gneissic rock. In the following analyses by F. A. Genth,
PEGMATITES OF THE MIDDIffiTOWN! AREA, CONTSTIECraCUT 671

analysis 1 is for a sample collected by J. D. Dana, and 2 is for a 

sample washed by Bradford's machine (table 16). Another analysis, 

made at Yale University, showed the nickel content about 3 percent 

lower than Genth's analyses. It was stated that the Genth analyses 

gave evidence of presence of the molybdenum group, and that too 

little material was present for a determination.

TABLE 16. Analyses of nickel-cobalt ore from Cobalt, Conn. 

[Analysis by F. A. Oenth]

Nickel ____ _______ __ _. _ __________________

Cobalt. __ __ _ __ _ ______________ __ ....

Iron. ____________ __ ___ ___________________

Sulfur _________________ ___ _ _

Total _______________________

i

9.44

3.82

11.85

4.78

70. 11

100. 00

2

10.17

3.85

12.92

5.62

1 67. 44

100. 00

i From loss by Ignition.

It is not known whether the last mining company failed because of 

lack of capital, inability to separate the cobalt from the nickel, 

arsenic, and iron, or from exhaustion of ore. The extant reports 8 

imply that the failure may have been from the first two causes. Since 

the ore apparently was confined to small shear zones within the Bolton 

schist, the quantity of ore would at most be very small by today's 

standards.

After the site was acquired by the State of Connecticut, a mining 

engineer examined the prospect for the State Development Commission (Bancroft,Howland, written communication, 1941). Thirteensamples from the seven available openings of the old workings were assayed 

and found to contain no cobalt or nickel other than a trace of cobalt 

in two samples. Arsenopyrite was the only metalliferous mineral 

found to occur within 15 feet of the surface. Rock samples were 

included for assay, since the older reports describe disseminated ore 

in weathered schist.

The writer could find no veins such as were described a century 

before. From the inclined shaft that was still open, two stopes 

extending about 40 feet below the surface were accessible in 1950.

* Francfort, E. 0., 1853, Unpublished report on the mines of the Chatham Cobalt Mining Co., Middle* 

town, Conn.

Francfort, E. 0., July 1855, Unpublished report of Prof. Jas. C. Booth and Second annual report of Dr. 

E. C. Francfort to the president, trustees, and stockholders of the Chatham Cobalt Mining Co., Middletown, Conn.; map of the Chatham Cobalt Mining Co. property, Cobalt, Conn., Llth. by Robertson & 

Selbert Co., 120 Fulton St., New York.
672 OOOSfTRIBUTTOnSflS TO ECONOMIC GEOLOGY

No metalliferous minerals were visible there; very small veinlets of 

quartz parallel the foliation of the schist. No sulfide minerals were 

visible within the main adit, which was blocked about 45 feet from 

the portal, or within the Engine shaft, which was then choked with 

debris. The engine shaft is known to be 120 feet deep, at which depth 

a crosscut was made southward for about 120 feet.

Tests with a small, portable Geiger counter showed counts per 

minute, as follows: The background count over the entire hillside for 

several hundred yards around the workings was 24-43 per minute; 

anywhere within the stopes, 15-40 feet below the surface, it was 

59-67; at the small opencut with the instrument held against the 

arsenopyrite flakes, the only sulfide mineral visible within the area, 

it was 21. At localities several miles removed from Great Hill, the 

background count was 12-15.

Because the increased rate of impulses could not be correlated with 

nearness to any body of rock, it was inferred that the increased count 

near the old workings was caused by extremely diffuse gaseous disintegration products and that the presence of uranium is not necessarily indicated. Old specimens of ore from the working face of the 

mine, now in the Wesleyan Univerity Museum at Middletown, gave 

no reaction with the portable counter used.

Mineral identification and radioactivity analysis in the Geological 

Survey laboratories gave these results on two of the Wesleyan specimens that were sawed and polished:

Wesleyan sample 3005

U. S. Geol. Survey lab. No.: 48116 

Equivalent uranium: 0.006 percent 

Minerals:

(1) pyrite, FeS2

(2) chalcopyrite, CuFeSa

(3) mineral whose composition and X-ray pattern place it midway between 

arsenopyrite, FeAsS, and lollingite, FeAsj

(4) staurolite, biotite, and plagioclase

Wesleyan sample SOU

U. S. Geol. Survey lab. No.: 48117 

Quivalent uranium: 0.002 percent 

Minerals:

(1) gersdorffite, NiAsS

(2) niccolite, NiAs

(3) chlorite and quartz

SILVER AND LEAD

Argentiferous galena was mined before the American Revolution 

at a now-caved working in the Bolton schist on the south bank of the 

Connecticut River (pi. 56). Whitney (1854, p. 393-394) describes
PEGMATITE© OF THE MIDDUETOWN AREA, CONNECTICUT 673

120-foot-deep workings made there in 1852-54. He reports that a 

vein 1^-3 feet wide contained 25-75 ounces of silver per ton of rock. 

Gangue included mostly quartz, some calcite, a very little barite, 

fluorspar, pyrite, and chalcopyrite. In 1949, minute quantities of 

fine-grained galena were found in outcrops of silicified Bolton schist 

near the abandoned workings. The area of the abandoned silver-lead 

prospect is within the crushed zone adjacent to the Triassic boundary 

fault.

BUHJMNG STONE

Stone from four of the rock units mapped in this area has been used 

for construction: the Monson gneiss, Maromas granite gneiss, Glastonbury granite gneiss, and sandstones of the Newark group. The 

only active quarry in the area in 1950 was the Tower Hill Granite 

Co. quarry, close to State Route 2 in the northern part of the area 

mapped (pi. 56). One or two workers at this quarry still cut replacements for old stone curbing from the Glastonbury granite gneiss.

Fifty years ago the cut-stone business in this area and throughout 

the State was an important industry. The decline of stone quarrying 

as concrete and other building materials became more widely used has 

resulted in a near cessation of the building-stone industry. Because 

most of the former quarries are now abandoned and full of water, 

complete descriptions of the building-stone and local quarries are 

left to older publications (Dale and Gregory, 1911).

The Monson gneiss was quarried in the 1890's just south of the 

Middle Haddam quadrangle. Westgate (1902, p. 5-6) described the 

rock at these quarries as a uniform dark-gray gneiss that has partings 

several feet apart along parallel veinlets of quartz. The stone was 

used for curbs and block pavement. Some care was necessary to 

avoid intercalated bands of dark minerals.

The description given by Dale and Gregory (1911, p. 116-117) for 

the Peterson quarry in the town of Bolton is believed to apply to 

Monson gneiss, although the quarry was listed as being in Glastonbury 

granite gneiss. Dale and Gregory state, "The stone is used for underpinning, cellar stone, etc." Presumably this was because the stone 

changes color upon exposure to weathering.

The Maromas granite gneiss was extensively quarried at the 

Maromas quarry, several Benvenue quarries, and many smaller 

openings. Railroad grades remaining show how the cut stone was 

shipped on railroad cars directly from the major quarries to purchasers. 

A smaller body of the same rock was quarried from a pit beside Great 

Hill Pond Brook north of the river near Cobalt. From this small 

quarry (pi. 56) came part of the stone used in construction of the 

railroad bridge above the brook a few yards away, where it can be 

seen today.
674 OONTRIBTJTKXMS TO ECONOMIC GEOLOGY

Westgate (1899, p. 654) writes of the Maromas granite gneiss, 

"It is handsome when first quarried, but stains quickly, and so is of 

use only for foundations, etc." A good description of the occurrence 

at the Benvenue quarries is given by Dale and Gregory (1911, p. 

76-78).

A description of several quarries opened in the Glastonbury granite 

gneiss is also given by Dale and Gregory (1911, p. 62-67). This 

distinctly foliated rock varies considerably from one locality to another 

in its appearance. In 1950 the Tower Hill quarry, 3.5 miles southeast 

from the Glastonbury, Conn., traffic circle, was producing a light-gray 

porphyritic stone for curbings, as mentioned above.

The sandstone of Triassic age was shipped in large quantities from 

the immense quarries in the city of Portland during the latter half of 

the 19th century. The finer grained layers of sandstone are well 

adapted to splitting with wedges, and this rock forms a durable 

building material provided the bedding planes of the rock are laid 

horizontally in the masonry. The site for quarries in this formation 

had to be carefully picked to avoid the numerous areas of pebble and 

cobble layers that prevent easy splitting. The use of brownstone 

declined because it weathers easily when laid with the parting surfaces 

vertical, and because the dark color also became unpopular.

SAND AND GRAVEL

Areas covered by glacial outwash of sand and gravel are shown on 

plate 56. All these areas are covered to a depth of more than 5 feet, 

although most of the deposits are thicker, as at Butler's (pi. 56) sand 

pit and others. There is an abundance of buff sand and gravel in 

the area that is suitable for many uses after size sorting.

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Wright, F. E., and Larson, E. S., 1909, Quartz as a geologic thermometer: Am. 

Jour. Sci., 4th ser., v. 28, p. 438.

Zodac, Peter, May 1937, Minerals of the Strickland quarry: Rocks and Minerals, 

v. 12, no. 5, p. 131-144.

 1941, The Andrews quarry near Portland, Conn.: Rocks and Minerals, 

v. 16, p. 164-167.

INDEX

A Page

Abstract..___.______________ 613-614 

Acknowledgments. ___.._ ..._ 617 

Age of pegmatites . 650-652 

AlbHer ....._.. _ . 642,643,658

Allanlte crystals ..._...... 629

Amphibolite....................... -..... 620.635

Anderson No. 1 mine..______ . 648 

Andeslne_____________...____ . 627 

Andrews quarry _____.. .. 648 

Anortbite_____*........................ 643

Apatite.. .................................... 658

Arsenopyrite.:________.__....___ 670

B

Banded and mammlllary structure. ____ 656 

Barlte . ______ ...._ 673 

Bear Hill, pegmatites near_____.____ 641 

Belltown Hill, Glastonbury granite gneiss at. 625,629 

Benvenue quarry, Maromas granite gneiss

at........................... 630,673,674

Beryl-________...__-______- 614,621,

640, 641,646, 648, 650. 654,655, 658, 666-668 

Bibliography...........______.._... 674-679

Biotite (see also Mica).............. 621,627,640,644

Bolton Notch, type locality of Bolton schist... 620 

Bolton schist.........__...___.... 619,620-626,

629,633,635,637,638,639,640,641,649 

Border zones_________________ 648 

Building stone________________. 673

O 

Calcite........_.........._______.__ 673

Carboniferous rocks, middle. _______._ 651 

Case No. 2 quarry..,_____________ 654 

Chalcopyrite__________________ 673 

Chestnut Hill, Monson gneiss at_.____ 635 

Clark Hill, Olastonbury granite gneiss at._. 627 

Cleavelandite......................._..... 643,648

Cobalt.....................___...._.... 670-672

Collins Hill, Bolton schist at._____^__ 620 

Maromas granite gneiss at.. _______ 633 

Columbite.___._______________ 647 

Concordant pegmatites..__________ 649 

Connecticut River, cross-axial course of.___ 618 

Connecticut Valley lowland. ___._____ 618 

Cores. ...__..___ ____ . 648 

Cramer pegmatite mine_____.____T .. 629 

Cretaceous rocks______________ 618,620

Deposits. (See Mines, prospects, and locali-

; . ties.)

Dikes............__. .... __.. 660

Dikes, dolerite.................... 620.638,640,652

DlopsidQ________.___________ 629

Page 

Discordant pegmatites_____............. 649

Distribution of pegmatites... 641 

Dome..________..._________... 639

E 

Kpidote.. . ...... . - 627

Erosion_.._..____.. ..__ 620

Faults.. ................................ 616, 618,

619,620,621,624,629,637,639,640,641,660,673

Feldspar, chemical analyses of______ 644

past production of..__________ 661-668

reserves of._______________ 614,669

Ftbrolitc... -.......... .................. 621

Fleldwork.. _____.___.________ 615-616 

Fletcher, J. D., analysis by ___ 667 

Fluorspar.. . . 678 

Folding... ................................ 639

Fossils.... .. .. - 637

Fracture fillings (see also Origin)___ 648,656

Galena...._____.__. ...___ 670,672

Oarnet................. 620,621,635,638,644,650,658

Qenth, F. A., analysis by.. 671

Geology . . . 619-639

Bolton schist......__ ......... .. 619,

620-626,629,635,637,638,639,640,641,649

Glastonbury granite gneiss.. . 619,

620,627-630,637,639,640,649,652,673

maflc gneiss unit... 619,624,629,639,641,649

Maromas granite gneiss... 619,

620,621.630-634,640,653,673

Monson gneiss.. 619,620,634-636,640,649,673

Newark group.._____._.__ 637-638,673

pegmatites-__.__ . 637

Pleistocene deposits_________ 638-039

Gillette quarry....________.._.... 643,644

Olaciation.. ............. .... 618,620,624

Glastonbury, Glastonbury granite gneiss at.. 627

Qlastonbury granite gneiss.. ____ 619,

620,627-630,637,639.640,649,652,673

Gotta Walden quarry........ __.. 629,649

Gravel and sand.__ 674 

Great Hill, Bolton schist at... 621

 Glastonbury granite gneiss at____ 619 

Great Hill Pond Brook, Maromas granite

gneiss at __.__._..... 633,673

Hale quarry ............. 616,642,653,656,657-659

Hebron gneiss...____ i ... 619

History, geologic. 620 

Homocline- _.......... ... 639

Hornblende.._______.______ 619,620,627 

HoweNo. 1 quarry...________ 616,644,659-660 

Hydrothermal alteration. (See Origin.)

681
682 INDEX

I Page

Igneous rocks__ ______ . 620 

Intermediate zones._______ . _ 648 

Introduction. ________________ 614-619

Katz, P. J., analysis by_____ __ 669 

Klllingworth dome.____ 619,620,624,634,635..6S2 

Kyanlte_______-_____ ..... 620,621

Larson Hill, Glastonbury granite gneiss at 629 

Lead. ... . , . 672-673

Lepldollte __ 643,648,662

M

Mafic gneiss unit.___ 619,624,629,639,641,649 

Marble . . 620,621

Maromas granite gneiss 619, 

620,621,630-634,640,653,673 

Maromas quarry, Maromas granite gneiss

at 630,673

Merlden formation-. ___ .. 638 

Metamorphlc rocks...... . 620

pegmatites in. . .... 614

publication describing cited.... _ 616

Metasedlmentary rocks____________ 619 

Metasomatism (see also Origin)... .... 616,650

Mica (see also Muscovite and Biotlte) 655,669

past production of____-_ ____ 665

scrap, reserves of._;__________ 614,669

Mlcrocllne _..._____________ 627,631

Middlctown formation . . . 649

Mlgmatlte __._______.____... 619

Mineral assemblages in pegmatites. _____ 648

Mineral resources (see also Minerals) 666-674

nonpegmatite minerals____-____ 670-674

building stone_______ ___ 673-674

cobalt.............................. 670-672

lead ............................. 672-673

nickel-__-___________ 670-«72 

sand and gravel_____ . __ 674 

silver....___________.__ 672-673

pegmatite minerals. ...... . 666-670

beryl . 666-668

feldspar...._._____ ___ 669

mica 669 

quartz.,.. ...._ __ 670

Minerals:

alblte............................... 642,643,658

allanlte crystals. 629 

amphibolite-. ___:.............. 620,635

andeslne.__ _______.____ 627 

anorthite ..____ ...__ 643 

apatite . .... 658

arsenopyrite ____________ 670 

barite..__-_______________ 673 

beryl. . 641,646,648,650,664* 656,658,666-668 

biotite (see also Mica).......... 621,627,640,644

calclte.___________________ 673 

chaleopyrite_______________ 673 

deavelandite - --------- 643,648

cobalt. ..-. 670-672

columbite___________......__.. 647

Minerals Continued

diopside ______ _...____ 62& 

epidote 627 

feldspar- .______ . 614,644,661-666,66» 

flbrolite.-__-____.._..__..__ 621 

fluorspar 673 

galena 670,672 

garnet________ 620,621,635,638,644,650,658 

hornblende-____.____-__ 619,620,627 

kyanite ^ - * ...__ 620,621 

lepldollte_*_-___- ... 643,648,652 

mica (see also Muscovite and Biotlte) 614,

655,665,669

mlcrocline * ... - 627,631 

morganlte ^ i. .. i 64ft 

muscovite (see also Mica) 644,650,660 

nlccolite- .~. . - 670 

nickel.., -. 670-672

nonpegmatite. (See Mineral resources.) 

oligoclase - .. 627 

pegmatite. (See Mineral resources.) 

perthite. ... ..... 642,643,644,648

plagioclase.___-___ ..____ 616,648 

pyrite.. - - 67* 

quartz..__ 614,621,627,631,642,644,648,653,670 

rutOe..... ..... ................ 621

samarskite._..____..."__....'._ 660,661

scorodite..._...___ ..._.. 670* 

sillimanite ___:_______.__ 621 

smalthlte-chloanthite_.... _____ 670-

sphalerite . . ; 670 

staurolite crystals______________ 621 

tourmaline-.._:.. 621,638,640,644,650,657,658- 

zircon.... ....... ...... 621

Mineralogy of pegmatites .. 642,647

Mines, prospects, quarries, and localities:

Anderson No. 1 mine.- ..... 648-

Andrews quarry._.... ........ 64&

Bear Hill 641

Belltown Hill........................... 627,62»

Benvenue quarry __ 630,673,674 

Bolton Notch............................ 620

Case No. 2 quarry_.. 654 

Chestnut Hill.-..... . __....... 636-

Clark Hill.............-.- ............ 627

Colllns Hill 620,633

. Oramer pegmatite mine. ..'...... 62*

Gillette quarry....___......_.__ 643,644

'*' Olastonbury_.___.. ....___.. 627

Gotta Walden quarry.... ......... 629,649

Great Hill. ................__ 619,621

Great Hill Pond Brook___.____ 633,673 

Hale quarry. . 616,642,653,656,657-659 

Howe No. 1 quarry_. 616,644,659-660 

Larson Hill .. 629 

Monson quarry_____ ____._,. 619 

Peterson quarry._ ...................... 673

Portland--- . 627

Bearing Brook....__.....__.____. 629

South Glastonbury._i________ 620,624 

Spinelli prospect...._... . 660-661

spodumene_______ ... ...... 643

State Forest No. 2 quarry 648 

Straits... 620,621

Strlckland pegmatite. 639 

Strickland-Cramer quarry.. 616,642,644,648,666
INDEX 683

Mines, prospects, quarries, and localitiesContinued

Tower Hill Granite Co. quarry.. 673,674 

Wannerstrom quarry_ . 666 

White Bocks............. ..... 618,641

Wlarda quarry .... 649

Mlsslsslppian rocks...'.______ 651 

Monson gneiss..... . 619,620,634-636,640,649,673

Monson quarry___________ C19 

Morganite _.......__.__ . 646

Muscovite (see also Mica)____ 644,650,060

N 

Newark group.................. 619,620,637-638,673

New Haven arkose .. .. .. 637 

Nlccollte.......... ....... ...... ............ 670-672

Nickel.. . .. 670,672

Ollgoclase_____._______ ...... 627

Origin of pegmatites_______.._... 652-657

Paleozoic rocks, pegmatites In.._ 614 

Faragenesis of minerals, Strlckland-Cramer

quarry . 616 

Pegmatite minerals. (See Mineral resources.) 

Pegmatites.____...__..... .... 640-665

age. 650-652

deposits....__...__........ - 657-665

distribution.. ____.__...__.. 641 

Hale quarry............ 616,642,653,656,657-659

Howe No. 1 quarry...__...... 616,644,659-660

internal structures_ .__ 647-649 

mineralogy.___________ _ 642-647 

minerals._______..__ 641 

origin.............. 652-657

production, past_ 661-665

shape_ 641 

size.. - 641

Splnelll prospect . 660-661 

temperature range of.____ . 653 

terminology . 641 

textures of____.___-_ 655 

wallrock, relation to 649-650,656 

water content of 653 

Perthite ............ ... 642, 643, 644, 648

Peterson quarry 673 

Physiography. 618 

Plagioclase. 616,648 

Portland, Glastonbury granite gneiss at 627 

Portland formation.. . 638 

Pre-Misslsslppian rocks 619 

Pro-Pennsylvania rocks. See Bolton schist. 

Pre-Silurian rocks, Monson gneiss 635 

Previous work 616-617 

Production of pegmatite minerals, past 661-665 

Pyrlte ................................. 673

Q

Quartz__.__..... 627, 631, 642, 644, 648, 653, 670 

massive lenses of. . ' 621 

reserves of . 614, 670

Page

Quartzlte, outcropping of at Great Hill.__ 620, 621 

Quaternary sand, gravel, and alluvium_ . 620

B

Replacement, metasomatic, theory of In paragenesis of minerals at StrlcklandCramer quarry__________ 616

Replacement bodies___; _______ 648,649

Roaring Brook, Glastonbury gneiss at____ 629 

Pleistocene deposits at__________ 638

Rutile - _..._._.__.___._ 621

S

Samarskite. ...________.__ 660,661 

Sand and gravel __ . 674 

Scorodite . 670 

Sedimentary rocks. ___________ 618,619,620 

Shape of pegmatites ...____... 641 

Sillimanite variety flbrollte_________ 621 

Silver-. . ... . 672-673 

Size of pegmatites ..______... 641 

Smalthite-chloanthlte. ___ . 670 

Sorby method_________________ 663 

South Glastonbury, Bolton Schist at____ 620

mafic gneisses at. ____.... 624

Sphalerite..._-_____-_____._._ 670 

Spinelli prospect .._._______ 660-661 

Spodumene-- 643 

State forest No. 2 quarry ______.... 648

Staurolite crystals_______________ 621 

Stock.. ___...___________.. 619,633 

Stone, building ......... ..._....__ 673-674

Straits, Bolton schist near_________ 620,621 

Strickland pegmatite ___ 639 

Strickland-Cramer quarry___ 616,642,644,648,666 

Structure... _________ 639-640

pegmatite, Internal ___.. 647-649

Terminology of pegmatites__________ 641 

Textures of pegmatites 642,647 

Till.... _........____....... 620

Tourmaline- .... 621,638,640,:644,650,657,668

Tower Hill Granite Co. quarry._____ 673,674 

Triassic rocks..... ......____ 620,637,674

early Late _.____________ 619 

fault boundary of_ _______.... 616,

618,619,620,621,624,637,640,673 

Tuff.___ .._________________ 620

W 

Wallrocks ____ ____ 663,666,658,659

relation of pegmatites to ...__ 649-660 

Wall zones.._._______________ 648 

Wannerstrom quarry __________ 656 

Wells, R. 0., analysis by___________ 669 

White Rocks area..._____________ 618

pegmatites near. _______._ 641 

Wlarda quarry_________________ 649

Zircon..... ........._____..._. 621

Zones, types of In pegmatites________ 647

o