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1038
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MINERAL RESOURCES.
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for
information on moss agate and mocha stone occurrences in Montana; Mr.
F. M. Myrick, of Randsburg, Cal., for specimens of St. Stephen stone
for examination; Mr. F. C. Faxon, of Silver Lake, Cal., for specimens
of copper-stained and amethystine chalcedony; Mr. Maynard Bixby, of
Salt Lake City, Utah, for specimens of jasperlike chalcedony; Mr. W.
B. Penniston, of Ashland, Oreg., for specimens of chalcedony and agate
and notes on the localities; Mr. F. H. C. Reynolds for notes on
occurrence of aquamarine near Royal-ston,Mass.; and Mr. George L.
English, of Shelby, X. C, for information on emerald occurrences in
North Carolina.
AGATE. MONTANA.
Moss
agate and mocha stone of fine quality occur in Montana. The agates have
been found chiefly on the west side of Yellowstone River from the
Dakota line up to and (reported) above Yellowstone Park. They range
back from the river over many miles of country, where they are gathered
by the ranchers and sheep herders. The agates are distributed over the
surface of the ground, in the gravel along creek and river beds, and
over some of the grass-covered buttes. The ones collected all lie at
the surface or only partly buried. They occur in pebbles, cobbles, and
in rough masses ranging from the size of a hazelnut to pieces weighing
12 pounds. Chemical tests made on a number of the black and
reddish-brown spots broken from rough specimens showed the presence of
both manganese and iron, confirming the generally accepted idea as to
the nature of the dendrites in mocha stone.
The
rough specimens of agate examined consist of fragments and a chipped
pebble more than 2 inches thick. The rounded form of the pebble may be
due in part to the shape of the cavity in which the agate was deposited
and in part to attrition during transportation along with the
associated gravels. The interior of the pebble and the fragments of
agate consist of translucent gray to blue-gray chalcedony. Some of it
shows a banded structure, and some an even texture. Black and brown
dendritic spots are scattered irregularly throuh the agate and in
places there are seams and irregular patches of the same color.
Reddish-brown, red, and bright-red dendrites, banding, and other
markings also occur in the agates. The texture of the dendrites ranges
from cloudy patches to branching tufts and fibers as delicate as those
found in the finest moss and ferns.
By
taking advantage of the arrangement of the dark seams and dendritic
patches, patterns are obtained that resemble moss, sea growths, ferns,
rushes, trees, and even landscapes with water and islands. The cut gems
consist of stones suitable for use in brooches, stick pins, watch fobs,
belt buckles, etc. The markings were present in different shades of
red, reddish brown light brown, dark brown to
black.
Three
specimens cut into fob gems displayed very attractive markings. One of
the fobs measuring 15 by 18 millimeters contained numerous black spots
2 to 3 millimeters in diameter, and one larger dendrite, 8 millimeters
across, resembling a sunflower. Another fob stone 27 by 31 millimeters
gave the effect of a small landscape, such as an overgrown garden with
untrimmed shrubbery, hawthorn, or
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