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Ch. 21: Stones Seldom Used as Jewels

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166            PRECIOUS STONES
colored in places or speckled with small white spots. Hard­ness, 6; specific gravity, 2.4 to 2.6. Acids do not affect it, nor does it yield readily to the blow-pipe. It consists of silica, alumina, lime, and soda. It is cut en cabochon and drop shape for brooches and pendants. Subtranslucent.
Apatite is named from the Greek apatad, to deceive, from an early misunderstanding of its nature. It occurs in Europe and the United States, and is found as hexagonal prisms, also massive and of compact fibrous structure. Trans­parent crystals of green, pink, and violet, resembling tour­maline, have been found in Maine. Hardness, 4.5 to 5 ; spe­cific gravity, 3 to 3.2. Lustre resinous, but somewhat greasy; transparent to opaque. It is composed principally of sub-sesquiphosphate of lime. Dissolves slowly in nitric acid, but is infusible under the blow-pipe. Some small crystals are transparent and colorless, but it is usually green. It is probably derived from animal fossils, as its constituents are contained in animal bones and ligaments. It is too soft to cut successfully. Some phosphoresce when heated, and become electric by friction.
Aragonite is named after Aragon in Spain, where it was originally found. It is the " satin spar" sold to tourists at Niagara Falls, and is imported from Wales. An amber and brown variety is called " California onyx." Crystallization trimetric in rhombic prisms. Hardness, 3.5 to 4; specific gravity, 2.9 to 2.10. Lustre vitreous; transparent to trans­lucent. Cleavage parallel to faces of rhombohedron. Same composition as calcareous spar: lime, 56; carbonic acid, 44. Falls to powder before the blow-pipe; effervesces with acids; phosphoresces when heated. Color, white with tinges of gray, green, yellow, and violet.
Axinite, called also thummerstein and thumite from Thum in Saxony, is found in Europe and the United States. Crys­tallization triclinic, in acute oblique rhomboidal prisms. It is remarkable for the sharp, thin edges of its crystals. Hard-
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