Formula: Ca2(Fe,Mg)3(Fe,Al)Al(Si6Al2)O22(OH)2
Origin of name: From ferrous iron (Fe2+) and tschermakite
Crystal system: Monoclinic
Crystal class: 2/m
Twinning:
Unit cell: = 9.818, b = 18.106, c = 5.331, β = 104.95°
Colour: Green, dark green, black
Diaphaneity: Translucent to nearly opaque
Luster: Vitreous
Habit: Crystals short prismatic; massive; compact
Hardness: 5 to 6
Specific gravity: 3.34
Cleavage: 3; {110} perfect, {001} and {100} parting
Tenacity: Brittle, conchoidal fracture
Streak: Greenish gray
Synonyms/varieties:
Comments: Series with tschermakite and with aluminotschermakite
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