loped in
advance of actual mining; but estimates based on past experience
indicate great potentialities of this region for future production.

In eastern Wyoming is a unique deposit of uranium ore in a quartzite
which lies between mica-schist and granite. The principal ore mineral is
uranophane, a hydrated calcium-uranium silicate, which is believed to be
an oxidation product of pitchblende. Some of the ore runs as high as 4
per cent uranium oxide, and the ore carries appreciable amounts of
copper but very little vanadium.

Very recently radium ores have been discovered in the White Signal
mining district of New Mexico, which was formerly worked for gold,
silver, copper, and lead. The radium-bearing minerals are torbernite and
autunite (hydrous copper-uranium and calcium-uranium phosphates), and
are found in dark felsite dikes near their intersections with east-west
gold-silver-quartz veins. The possibilities of this district have not
yet been determined.

Pitchblende has been found in gold-bearing veins in Gilpin County,
eastern Colorado, and in pegmatite dikes in the Appalachians, but these
deposits are of no commercial importance. Pitchblende is grayish-black,
opaque, and so lacking in distinctive characteristics that it may
readily be overlooked; hence future discoveries in various regions would
not be surprising.

CHAPTER XIII

MISCELLANEOUS NON-METALLIC MINERALS

NATURAL ABRASIVES

ECONOMIC FEATURES

Natural abrasives are less important commercially in the United States
than artificial abrasives, but a considerable industry is based on the
natural abrasives.

Silica or quartz in its various crystalline forms constitutes over
three-fourths of the tonnage of natural abrasives used in the United
States. It is the chief ingredient of sand, sandstone, quartzite, chert,
diatomaceous earth, and tripoli. From the sand and sandstone are made
millstones, buhrstones, grindstones, pulpstones, hones, oilstones, and
whetstones. Sand, sandstone, and quartzite are also ground up and used
in sand-blasts, sandpaper, and for other abrasive purposes. Chert or
flint constitutes grinding pebbles and tube-mill linings, and is also
ground up for abrasives. Diatomaceous (infusorial) earth is used as a
polishing agent and also as a filtering medium, an absorbent, and for
heat insulation. Tripoli (and rottenstone) are used in polishing powders
and scouring soaps as well as for filter blocks and many other purposes.