Formula: NaMg2Al3Si2O10(OH)2
Origin of name: for H. Preiswerk, Swiss mineralogist
Crystal system: monoclinic
Crystal class: 2/m
Twinning:
Unit cell:
Colour: pale green
Diaphaneity:
Luster:
Habit: plate-like grains, to 1 mm, nodular aggregates
Hardness: 2.5
Specific gravity: 2.96
Cleavage: 1; {001} perfect
Tenacity:
Streak:
Synonyms/varieties:
Comments:
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