Formula: []Ca2(Mg,Fe)3(Fe,Al)Al(Si6Al2)O22(OH)2
Origin of name: for Gustave von Seysenegg Tschermak, Austrian mineralogist
Crystal system: monoclinic
Crystal class: 2/m
Twinning:
Unit cell:
Colour: green, dark green, black
Diaphaneity: translucent to nearly opaque
Luster: vitreous
Habit: crystals short prismatic, twinning common, massive, compact
Hardness: 5 to 6
Specific gravity: 3.14 to 3.35
Cleavage: 3; {110} perfect, {001} and {100} parting
Tenacity:
Streak:
Synonyms/varieties:
Comments: series with ferrotschermakite and with aluminotschermakite
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