Ch. 2: Maine Pegmatites: Local Descriptions

Ch. 2: Maine Pegmatites: Local Descriptions Page of 170 Ch. 2: Maine Pegmatites: Local Descriptions Text size:minus plus Restore normal size   Mail page  Print this page
52                 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
in graphic intergrowths with quartz. As described below, some, small clear muscovite prisms are surrounded by a border of lepidolite. Mr. Lamb has also found some fine curved crystals of muscovite.
Biotite is abundant only locally and can in most areas be readily avoided in mining the feldspar. It forms typical lath-shaped crystals.
Lepidolite is not very abundant, but some occurs especially asso­ciated with clevelandite and muscovite near pockets. It is present in granular aggregates of small plates and prisms (in many places intergrown with some quartz) and also in larger plates. Its occur­rence as narrow borders surrounding muscovite and in crystallo-graphically parallel growth with it has been fully described and figured by Clarke,a who gives analyses of both of the muscovite and the lepidolite border.
Garnets of small size occur sparsely in all parts of the pegmatite. They are most abundant in the more quartzose and micaceous parts and are not present in injurious amounts in the more highly feld-spathic portions.
Black tourmaline is present in all those portions of the pegmatite which carry colored tourmalines but is only locally abundant and is not particularly bothersome in feldspar mining. Most of the colored tourmalines which have been obtained have come, not from the feldspar workings, but from small pits near the Hatch farmhouse, worked at an earlier date solely for their gems and mineral specimens. Those found in 1883 by N. H. Perry ranged from 1 centimeter to 10-1/2 centimeters long, and differ from the majority of the Maine tourmalines in being mostly of lighter color. They were found colorless, light pink, lilac, light blue, light puce colored, bluish pink, and light green, some single crystals showing nearly all these colore. Gems from some of the paler crystals are said to have deepened very much in color after cutting. The majority of these crystals, of which nearly 1,500 were obtained, were more or less flawed. Some of the tourmalines found later by Mr. Lamb were cut into gems of emerald-green color.
Crystals of light bluish-green beryl also occur rather abundantly, embedded in the solid pegmatite. One hexagonal beryl found about 1898 is reported by J. S. Towne to have been 4 feet in diameter and 20 feet in length, but the majority do not exceed 1 foot in length and a few inches in diameter. Near the gigantic beryl mentioned occurred several pockets bearing the finest crystals of herderite ever found on Mount Apatite; the form and composition of these have been described by Penfield.6
Apatite occurs occasionally in crystals of fine luster and trans-parency, the colors being light pink, purple, light blue, and blue
Ch. 2: Maine Pegmatites: Local Descriptions Page of 170 Ch. 2: Maine Pegmatites: Local Descriptions
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