APPENDIX 5. 

 INDUSTRIAL USES OF PRECIOUS STONES. 1 



In the following paragraphs are mentioned 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 stand- 

 ardization (for example, fluorite and quartz as standards of densities 

 and of refractive indices), and as sources of material for investiga- 

 tion, 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 han- 

 dles, paper weights, and pipes (meerschaum). 



^gate.— Mechanical bearings and supports, scale bearings, balls for water meters, mor- 

 tars for laboratory use, spatulas, paper knives, playing marbles, and small orna- 

 ments. 

 Azurite— Ore of copper; pigment for paint. 

 Azurmalachite. — Ore of 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 lar«.e 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 pelluci 1 



i Dr W T Schaller, Mineral Resources of the United States, 1918. 



205 



