Hollister prospects, South Glastonbury, Glastonbury, Hartford County, Connecticut, USAi

Regional Level Types
Hollister prospects	Group of Prospects
South Glastonbury	Village
Glastonbury	Town
Hartford County	County
Connecticut	State
USA	Country

"The prospect is on a tract of 30 acres owned by Dino L. Bertolini, 815 State Street, New Haven, Conn. The property is said to have been worked briefly for feldspar about 1930. It was prospected for feldspar and mica for several months in the spring of 1943 by Fausto Bertolini, 815 State Street, New Haven. The property was mapped by E. N. Cameron and V. E. Shainin in March 1943 (fig. 122). At that time the workings consisted of seven small excavations. The northernmost and largest was an opencut 65 feet (ca. 20 m) long, 20 feet (ca. 6 m) wide and 15 feet (4.57 m) in maximum depth.

Three pegmatites, each striking due north, are shown on figure 122, but the northern pegmatite may be connected with either the southernmost or the middle pegmatite. The wallrock is Monson gneiss, the foliation of which strikes northward and dips gently westward.

Northern pegmatite. — The northern pegmatite, exposed for about 240 feet (ca. 73 m) along strike, has an outcrop width of about 25 feet (ca. 8 m). The pegmatite probably dips steeply eastward. The pegmatite is roughly parallel to the strike of the wallrock foliation but differs markedly in dip. The bulk of the pegmatite consists of medium- to coarse-grained quartz, [microcline] perthite, graphic granite, plagioclase [albite], in various proportions, with subordinate muscovite and accessory garnet [most likely almandine], tourmaline, beryl, and columbite-tantalite. In the south pits, this material seems to enclose small pods consisting of coarse [microcline] perthite, quartz, graphic granite, and muscovite, with minor plagioclase [albite], scattered crystals of beryl, and tourmaline, and traces of columbite-tantalite. In the quarry at the north end of the area mapped, a border zone 18 inches (ca. 46 cm) thick, consisting essentially of line- to medium-grained quartz and plagioclase [albite], lies along the west wall.

Near the east end of the headwall of the quarry and along the east wall, the pegmatite is cut by a tabular fracture-controlled replacement body, 4 inches (ca. 10 cm) to 2 feet (ca. 61 cm) thick. This body strikes N. 2° W. and dips 69° E., and extends across the headwall from top to bottom and northward along the base of the east wall to a point about 20 feet (ca. 6 m) from the headwall, where it passes under overburden. It consists of book muscovite, plagioclase [albite], and quartz. The east margin of the body is even, nearly straight, the west margin is highly irregular, as it is defined by the outer ends of muscovite books that project various distances into the adjacent pegmatite. The books are mostly arranged with cleavages perpendicular to the walls of the body or nearly so. In the overlying pegmatite a faint layering parallel to the fracture-controlled body is visible owing to alignment of small garnet [most likely almandine] crystals in discontinuous streaks. The garnet is associated with sugary plagioclase [albite], quartz, and small muscovite crystals, and the whole group of minerals appears to have formed by replacement of the perthite-plagioclase-quartz pegmatite.

In the headwall of the quarry the pegmatite is cut by a reverse fault that strikes N. 17° E. and dips 20° to 33° W. The apparent displacement along it is not more than a few feet. It is marked by a crush zone filled with gouge and fragments of pegmatite.

Muscovite books from the northern pegmatite range from 2 inches (ca. 5 cm) to more than 1 foot in diameter, and from ¼ inch to 4 inches (ca. 10 cm) in thickness. Most of the books are hard, and free splitting, but they are marred by ruling, cross fracturing, and, less commonly, by “A” structure. The books seem to contain a satisfactory percentage of sheet mica, but as they range from fair-stained to heavy-stained only a small part of the sheet recovered would be of No. 1 and No. 2 qualities. The stain is of the grating type and probably due to magnetite.

Beryl is unevenly disseminated through the [microcline] perthite-plagioclase [albite]-quartz pegmatite in green to yellow-green prisms in part intergrown with quartz and [albite] plagioclase, and as scattered crystals associated with the pod in the south pit. Most of the beryl is in crystals 0.1 and 0.4 inch (ca. 1 cm) in diameter and less than 1 inch (2.54 cm) long, but crystals as much as 2 inches (ca. 5 cm) in diameter and 4 inches (ca. 10 cm) long are present. A real measurement of 80 beryl crystals exposed in 142.9 square feet (ca. 13 m²) of the headwall of the northernmost cut indicated a beryl content of 0.09 percent…

Middle pegmatite. — The middle pegmatite is poorly exposed and has not been studied in detail. It appears to resemble the northern pegmatite in mineral composition.

Southern pegmatite. — The southern pegmatite is exposed at intervals for 160 feet (ca. 49 m). It is 4 to 9 feet (2.74 m) wide and seems to be almost vertical. Its walls are irregular. It consists of smoky quartz, [microcline] perthite, massive plagioclase [albite], cleavelandite, garnet [most likely almandine], beryl and traces of lepidolite and columbite tantalite. The mica occurs along small pods of coarse-grained quartz.

Mica in the southern pegmatite is similar to that from the northern pegmatite. Beryl, in crystals ¼ to 2 inches (ca. 5 cm) in diameter and ½ to 5 inches (ca. 13 cm) long, is associated with quartz and cleavelandite, and is very unevenly distributed. Measurements of beryl crystals exposed in 74 square feet (ca. 7 m²) of pegmatite indicate a beryl content of about 0.11 percent."