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:
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