Formula: K-Na-feldspar
Origin of name: from Greek for tablet
Crystal system: monoclinic
Crystal class: 2/m
Twinning: common by Carlsbad law, less common by Manebach or Baveno law
Unit cell: a = 8.43 Å, b = 13.00 Å, c = 7.17 Å, b = 116.1°
Colour: colourless, whitish, tan, pinkish
Diaphaneity: transparent to translucent
Luster: vitreous
Habit: crystals prismatic, often tabular
Hardness: 6
Specific gravity: 2.56 to 2.62
Cleavage: 6; {001} and {010} perfect, {100}, {110}, {-110} and {-210} partings
Tenacity: brittle
Streak: white
Synonyms/varieties: potassium feldspar, potash feldspar
Comments: K-Na feldspar with disordered Al-Si arrangement, trimorphous with microcline and orthoclase
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