|
672 MINERAL RESOURCES, 1913—PART II.
the jasper into pebbles and bowlders, which display their color and markings very well when wet.
The
jaspers show a wide range of colors, with both dark and i. red, yellow,
brown, and green. Some of the red and yellow jas are very bright
colored. A variety of markings or patterns are met with, of which the
most interesting is that called "kinradite," after J. J. Kinrade, of
San Francisco, who discovered and first used it for gems. This variety
shows spherulites, generally of one color, scattered through jasper of
another color. The spherulites are composed of radiated aggregates of
quartz, with concentric color bands in some specimens. The spherulites
resemble chalcedony, but under the microscope, between crossed nicols
they have the positive elongation characteristic of quartz. The
spherulites range in diameter from microscopic dimensions to over an
inch. In cutting kinradite the gem- may contain only one large
spherulite or there may be several spherulites of various sizes. Some
gems may contain 25 or more smaller spherulites. The colors, the
variations in texture, and the interesting structure of the spherulites
in kinradite render it an attractive gem and ornamental stone.
Some
of the other jasper found with kinradite is of good gem quality. Among
specimens seen were some showing very bright crimson red in small
streaks and patches through yellow and dark dull green. This would
yield gems showing the three colors in strong contrast. Almost
innumerable other color patterns can be cut from these associated
jaspers.
A
deposit of bloodstone and jasper was discovered by F. M. Myrick, of
Johannesburg, Cal., in the Death Valley region of San Bernardino
County, in February, 1908. Considerable prospecting since that time has
resulted in promising finds of gem minerals. Many cut gems have been
sold in several towns of southern California where they have been
favorably received.
The
deposit is about 45 miles northeast of Johannesburg and 4 miles S. 20°
E. of Brown Mountain in the rough mountains about 12 miles west of
Death Valley. Prospects have been opened over an area about 300 yards
across among the gulches at the head of three valleys draining west
and northwest. The prospects are at elevations of about 3,300 feet
above sea level, or 200 feet higher than the camp in the draw to the
west. The principal work consists of a cut, 15 feet across and 12 feet
deep, and a prospect tunnel in the side of a draw. Over a dozen other
pits have been made on outcroppings of bloodstone or associated jasper.
The
geology around the bloodstone deposits is complex. Basaltic lava and
andesitic rock predominate, but some sedimentary rocks are exposed
close to the prospects. The basalt is dark reddish brown, through the
oxidation of ferruginous constituents and quite vesicular in places.
The andesitic rocks are fine grained and in places thev are greenish
from the presence of epidote and chloritic alteration products. The
sediments consist of gray to white shaly calcareous rock with
interbedded sandy and sintery layers. These rocks contain fossil mud
cracks, ripple marks, raindrop marks, and a few markings resembling
worm tracks. A portion or the sediments contain pebbles and angular
inclusions, like a tuff or volcanic ash formation, and such is their
general appearance. It is probable that these rocks were formed as ash
beds in shallow pools or water. The carbonate of lime may
|
||
|
|
||