Ch. 3: Precious Gem stones in 1913

Ch. 3: Precious Gem stones in 1913 Page of 115 Ch. 3: Precious Gem stones in 1913 Text size:minus plus Restore normal size   Mail page  Print this page
GEMS AND PRECIOUS STONES.                              687
inches across, and many of them are aggregated around quartz crys­tals. The felsite has the appearance of growing secondarily around the larger crystals of the different minerals—that is, of filling portions of previously existing miarolitic cavities.
The majority of the topaz from the Await prospect is colorless and of beautiful transparency, but a little clear delicately tinted bluish topaz was also found.
The topaz prospect of Lee McGehee is about half a mile northwest
of the Await prospect in a flat along a dry branch. Shallow pits have
been dug over about an acre of ground on the west side of and a few
feet higher than the bed of the dry stream. The pits are scattered
here and there without any definite arrangement. The country rock
is the coarse porphyritic red granite characteristic of the region and
outcrops in flat ledges and large rounded bowlders. A coarse angular
gravelly soil formed by the decomposition of the granite covers much
of the surface. The topaz occurs in a bed of such soil which has been
transported a short distance only and deposited in its present position
along with coarser gravel and small angular bowlders. The wash
material has been deposited on disintegrated granite and because of
the sharp edges of its components it is difficult to determine the line
of demarcation between wash material and soil in place. So far all
the topaz has been found loose in the wash along with other minerals
commonly found associated with it. No gem pockets have been
found in the granite, though the topaz-bearing wash has not been
transported far from its source. Granite outcrops project above the
wash within 100 yards to the southwest, and the dry stream has cut
into the granite close to the topaz prospects. Among the minerals
which have evidently come from the topaz-bearing pockets are quartz
crystals, red, gray, and bluish-green microline feldspar, muscovite,
and a small quantity of cassiterite. A number of the dark smoky
quartz crystals one-half inch to 2 inches in diameter were coated with
a thin layer of reddish-gray microcline. Topaz of very good quality,
chiefly colorless but some of pale bluish-green tint has been taken
from the McGehee prospect. Many of the crystals have been partly
fractured or rounded by attrition so that they are not suitable for
fine cabinet specimens. Some large, imperfect transparent crystals
and fragments of crystals have been obtained, and among them the
■st topaz found in the county. This specimen is now in the col-
on of the United States National Museum. It Weighs 1,296
grams, or 45.7 ounces avoirdupois, and is mostly transparent and
colorless. Two opposite corners are tinted a faint bluish green. The
crystal has a large cleavage plane base, with some of the other faces
fairly well developed but partly dulled by etching and attrition by
sand and water.
The Amarine prospects are a few hundred yards southwest of the Await prospect. Three pits 8 to 15 feet deep were opened at one place, and another pit 12 feet deep was made about 200 yards to the prthwest. All of the workings are in hard rock and required blasting to open. In each opening red pegmatite was encountered in coarse porpnvritic red granite. In the southeast prospects large red micro-dine feldspar crystals, massive and crystal quartz, muscovite, black tourmaline, and purple and gray fiuorite were observed. In the north-westprospect a pegmatite vein with an east strike and a 10° S. dip was ffiposed in coarse red granite. This pegmatite inclosed a vein of gray
Ch. 3: Precious Gem stones in 1913 Page of 115 Ch. 3: Precious Gem stones in 1913
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US Geol. Surv. 1913. Gemstones, Metals.
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