Formula: Al4(PO4)3(OH)3.9H2O
Origin of name: for Rene Van Tassel (1916-), Belgian mineralogist of phosphate and sulfate minerals
Crystal system: Orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell: a = 10.528, b = 16.541, c = 20.373
Colour: White, pearl white
Diaphaneity: Transparent to translucent
Luster: Greasy, pearly
Habit: thin white lamellae forming rosettes to 8 mm
Hardness: 2 to 2.5
Specific gravity: 2.30
Cleavage: 1; {001} perfect, micaceous, {010} imperfect
Tenacity: Slight flexible
Streak: White
Synonyms/varieties:
Comments:
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