Formula: (Na, K)AlSi3O8
Origin of name: For Greek an = not, orthos = right (angle), and klan = to cleave
Crystal system: Triclinic
Crystal class: -1
Twinning: Common by Carlsbad, Baveno or Manebach law; also by Albite or Pericline law
Unit cell: a = 8.29 Å, b = 12.97 Å, c = 7.16 Å, a = 91.1°, b = 116.3°, g = 90.2°
Colour: Colourless, white, grey, yellowish, reddish, greenish
Diaphaneity: Transparent
Luster: Vitreous, somewhat pearly on cleavages
Habit: Crystals usually short prismatic, blocky, tabular; massive, cleavable, granular
Hardness: 6 to 6.5
Specific gravity: 2.56 to 2.6
Cleavage: 5; {001} and {010} perfect, {100, }{-110}, {-201}partings
Streak: White
Synonyms/varieties:
Comments: Feldspar (alkali) group, intermediate between low sanidine and high albite. Occurs in high-temperature sodic volcanic and hypabyssal rocks.
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