Formula: Na2SO4
Origin of name: For Louis Jacques Thenard (1777-1826), French chemist
Crystal system: Orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning: Common on {110}, contact, commonly forming cruciform groups, as crude butterfly-like twins on {011}
Unit cell: a = 5.863 Å, b = 12.30 Å, c = 9.821 Å
Colour: Colourless, grayish white, yellowish, brownish, reddish due to inclusions
Diaphaneity: Transparent to translucent
Luster: Vitreous to resinous
Habit: Crystals tabular, dipyramidal, rarely prismatic, to several cm, efflorescence, crusts
Hardness: 2.5 to 3
Specific gravity: 2.66-2.70
Cleavage: 3; {010} perfect, {101} fair, {100} incomplete
Tenacity: Uneven to hackly, splintery fracture
Streak: White
Synonyms/varieties:
Comments: Found in non-marine evaporite deposits in arid climates and alteration of alkali-ignous rocks protected from water. Soluble in water, taste slightly saline.
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