Description: once molten natural materials; amorphous in structure; chemical composition variable, but mostly silica; the types cut as gems include: obsidian (natural glass of volcanic origin). Appearance: • transparent to opaque, sometimes with sheen • gray to black (often spotted with white), brown to brownish yellow, orange, or red;rarely green, blue, purple• phenomena: iridescence, chatoyancy (rare) […]
Appearance: • semitransparent to opaque • virtually all colors Variety and Trade Names: • agate – chalcedony with curved or angular bands or layers • moss agate or mocha stone – chalcedony with green, black, or brown inclusions that look like moss• onyx – chalcedony composed of straight, parallel layers of different colors• sardonyx – onyx […]
Appearance: • semitransparent to opaque • virtually all colors Variety and Trade Names: • jasper – general variety term applied to semi translucent to opaque chalcedony of any color or combination of colors, except solid black or specially labeled material, such as bloodstone, onyx, etc. Stone Information from: Gem Reference Guide, by GIA, ISBN 0-87311-019-6 Gemstones […]
Description: Ruby is a variety of the mineral species corundum (ko-RUN-dum); hexagonal (trigonal) crystal system. Major Sources: Thailand, Burma, Kampuchea, Sri Lanka, Kenya. Appearance: • transparent to opaque• orangy red to purplish red, brownish red• phenomena: asterism, chatoyancy (very rare) Identification: Optic Character: DR, uniaxial negativeRefractive Index: 1.762-1.770 (+.009, -.005) Absorption Spectra: a strong doublet at […]
Description: The variety of the mineral quartz; hexagonal (trigonal) crystal system. Major Sources: Brazil, Uruguay, Namibia. Appearance: • Transparent; material used for beads and carvings may be translucent • Bluish purple to purple to reddish purple; often shows a slight shift in hue under different lighting Identification: Optic Character: DR, uniaxial positive Refractive Index: 1.544-1.553 (very constant) […]
Description: Almandite (ALL-man-dite) or almandine (ALL-man-deen) is a mineral species in the garnet group; cubic crystal system. Appearance: • transparent to semi-translucent (for very dark stones)• reddish orange to red, slightly purplish red to reddish purple: typically dark in tone Identification: Optic Character: SR, often ADR Refractive Index: 1.790 (3.030)Absorption Spectra: usually three strong bands at […]
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