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
106              PEGMATITES AND ASSOCIATED EOCKS OF MAINE.
in 1906, but in 1908 the quarry waste which had been clumped in it was being removed and new excavating had revealed considerable amounts of excellent feldspar. It is significant that much of the waste material dumped into this pit in the early mining is of good commercial grade according to present standards and is being saved. In the early days graphic granite was mostly discarded and only practically pure feldspar utilized. This pit is now about 100 feet in depth. The northernmost pit, from which large amounts of spar have recently been taken, is 200 feet long in a direction X. 25° E., 40 to 75 feet wide, and 20 to 30 feet deep.
In this quarry the commercially valuable rock is mainly a coarse graphic intergrowth of feldspar and quartz, which is estimated to comprise about one-half the total material excavated, the other half being waste which is highly quartzose or contains muscovite or iron-bearing minerals. (See Plate XVIII).
The quartz of this quarry is mostly gray and semiopaque, and in many places has a granular appearance. In a few places it is slightly pinkish in hue. Masses of pure quartz are usually small, the largest observed by the writer being a mass 6 feet across in the northern­most pit. It is not utilized commercially.
Most of the feldspar is orthoclase or microcline with small amounts of albite. The following analysis by the Pittsburg testing laboratory of the United States Geological Survey is of the best grade of buff-colored feldspar:
Very few large masses of pure feldspar are exposed in the present quarry openings, but it is said that in the past single blasts have loosened 100 tons of almost pure material. In the southern pit a number of masses of pure feldspar several feet across were exposed in 1908, but most of the rock here and practically all exposed in the middle and northern pits is an intergrowth of quartz and feldspar. Most of this intergrowth, however, is of excellent quality for pottery uses, since injurious minerals such as muscovite and black tourmaline are usually confined to certain portions of the mass and can be readily separated from the rest of the rock in mining. Although the graphic
Ch. 2: Maine Pegmatites: Local Descriptions Page of 170 Ch. 2: Maine Pegmatites: Local Descriptions
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