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Ch. 7: Quartz Group - Opal, Rock Crystals, Amethysts, Rose Quartz, Agate, etc.

Ch. 6: Beryl (Emerald, Aquamarine), Chrysoberyl, Phenacite, & Euclase Page of 364 Ch. 7: Quartz Group - Opal, Rock Crystals, Amethysts, Rose Quartz, Agate, etc. Text size:minus plus Restore normal size   Mail page  Print this page
CHAPTER VII.
The Quartz Group:—Rock Crystal, Transparent Quartz, Amethyst, Smoky Quartz,
Cairngorm Stone, Gold Quartz, Rose Quartz, Novaculite, Silicified Coral,
Quartzite, Quartz Inclusions, Thetis Hairstone, Agate, Jasper,
Silicified Wood, Opal, Hydrophane, etc.
T HE quartz group consists of a large series of substances, which to the eye are very unlike each other, and pass under a great variety of names, but. they are all chemically of one substance, namely, silica. The vari­ous colors are evidently due to the presence of metallic oxides, principally manganese or iron. Quartz may be divided into two groups, crystalline and cryptocrystalline. The former crystallizes in the rhombohedral system, generally as six-sided prisms, with a hardness of 7 and a specific gravity for the colorless of 2*65, the specific gravity of cairngorm and the amethyst being slightly higher.
Following is a list of the crystalline varieties : Amethyst.—Deep purple, bluish violet fading almost into pink.
Asteriated Star-Quartz.—Containing between layers of the crystals a deposition of substances, so that when cut en cabo-chon across the prism it exhibits asterism.
Aventurine.—Transparent to opaque, either red or yellow, with iridescent spangles of mica distributed through it.
Cairngorm.—Transparent, smoky gray, yellow, yellowish brown, and brown.
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Ch. 6: Beryl (Emerald, Aquamarine), Chrysoberyl, Phenacite, & Euclase Page of 364 Ch. 7: Quartz Group - Opal, Rock Crystals, Amethysts, Rose Quartz, Agate, etc.
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