Anorthite Archives - Cochise College Geology

Anorthite

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Chemical Group: Silicate (plagioclase feldspar)

Chemical Formula: CaAl₂Si₂O_8.Anorthite is the calcium end member of the plagioclase feldspars. Anorthite ranges from 0% to 10% NaAlSi₃O₈and 100% to 90%CaAl₂Si₂O₈.

Color: White, gray, reddish Transparency: Transparent to translucent

Streak: Uncolored Luster: Vitreous, pearly Tenacity: Brittle

Hardness: 6 to 6.5 Specific Gravity: 2.74 to 2.76

Fracture: Uneven to conchoidal

Cleavage: (001) perfect and (010) slightly less

Crystal Forms: Triclinic system. Crystals prismatic
Commonly shows polysynthetic (plagioclase) twinning.

Mineral habits: Massive, granular, coarse lamellar

Mineral Associations: Found in andesite, basalt, gabbro, norite

Identifying Characteristics: White color, plagioclase twinning

Occurrences: Franklin, New Jersey

Toxicity: When-swallowed: moderate When-inhaled: high

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