Formula: (Na,Ca,K)AlSi2O6 . 3H2O
Origin of name: For John Herschel, British astronomer
Crystal system: Hexagonal
Crystal class: -3 2/m
Twinning:
Unit cell: a = 1.99 Ǻ, c = 15.10 Ǻ
Colour: White
Diaphaneity:
Luster: Vitreous
Habit: Hexagonal plates in aggregates
Hardness: 4 to5
Specific gravity: 2.08 to 2.16
Cleavage: 1; {10-11} distinct
Tenacity: Uneven; brittle
Streak:
Synonyms/varieties:
Comments:
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