SOME INDUSTRIAL USES OF PRECIOUS STONES.
In
the following paragraphs are given some industrial uses of minerals of
gem quality. In addition to ornamentation, all gem minerals are of
value as specimens for collections, for use in standardization (for
example, fluorite and quartz as standards of densities and of
refractive indices), and as sources of material for investigation,
both industrial and scientific. These uses are therefore not always
repeated under the different mineral names. Ornamentation itself covers
a variety of utilization, such as for jewelry, knife handles, paper
weights, and pipes (meerschaum).
Agate. Mechanical bearings and supports, scale bearings, balls for water meters.
Azurite. Ore of copper; pigment for paint.
Azurmalachite. Ore ol copper.
Calcite. See Iceland spar.
Chromite. Ore of chromium.
Chrysocolla. Ore of copper.
Cobaltite. Ore of cobalt.
Corundum. See Sapphire.
Diamond. Cutting,
grinding, engraving, boring, and polishing material; supports for
bearings and pivots; dies for wire drawing; tips for phonograph needles.
Epidote. For coloring artificial slate and roofing material.
Fluorite. See Optical fluorite.
Franklinite. Ore of manganese and zinc.
Garnet. Abrasive; for watch jewels or jeweled bearings; as tared weights.
Garnierite. Ore of nickel.
Gypsum. Used in manufacture of artificial pearls—the so-called "Roman pearls."
Hematite. Ore of iron.
Iceland spar.—Iceland
spar is a variety of calcite, clear and transparent and unusually free
from imperfections and impurities. Transparent crystals or cleavage
pieces of calcite-of any appreciable size are very rare, and as Iceland
has furnished almost all of such material used, the name Iceland spar
has been given it.
Elongated
cleavage rhombohedrous of Iceland spar are used in the manufacture of
nicol prisms, which are an essential part of optical instruments
requiring plane polarized light, as, for example, certain microscopes,
dichroscopes; and sacchari-meters. The material, on account
of its simple chemical composition and purity, finds application in
chemical standardization. Iceland spar is also used in the manufacture
of some kinds of glass, and some of it is sold as mineral specimens.
Pieces
of Iceland spar, either in single untwinned crystals or parts of such
crystals, or in homogeneous untwinned cleavage rhombohedra, which are
large enough to yield a rectangular prism at least 1 inch long and half
an inch thick each way and which possess the properties described
below, are suitable for optical purposes. The colorless material must
be so clear and transparent that it is limpid and pellucid. It must not
be partly opaque on account of numerous cracks or fractures, must not
show any internal, iridescent, or rainbow colors due to
