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Roger Weller, geology instructor
Chemical Group: silicate (plagioclase feldspar)
Chemical Formula: CaAl2Si2O8 Anorthite is the calcium end member of the plagioclase feldspars.
Anorthite ranges from 0% to 10% NaAlSi3O8 and 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
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