Formula: (Na,K)AlSiO4
Origin of name: from Greek for cloud
Crystal system: hexagonal
Crystal class: 6
Twinning: on {20-10}, {11-22} or {33-65}
Unit cell: a = 10.06 Å, c = 8.417 Å
Colour: colourless, white, gray, yellowish, greenish, bluish gray, dark
Diaphaneity:
Luster: vitreous to greasy
Habit: crystals simple hexagonal prisms, massive, compact, embedded grains
Hardness: 5.5 to 6
Specific gravity: 2.55 to 2.67
Cleavage: 2; {10-10} and {000-1} indistinct
Tenacity: subconchoidal, brittle
Streak: white
Synonyms/varieties:
Comments:
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