Formula: (Mn,Mg,Ca,Pb)9(AsO3)(AsO4)2(OH)9.2H2O
Origin of name: from Greek for with and brother
Crystal system: orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning: fourlings
Unit cell:
Colour: colourless, red, reddish brown, dark brown or black
Diaphaneity: transparent to translucent
Luster: vitreous to adamantine, sometimes submetallic
Habit: crystals short prismatic, striated, twinned fourlings, massive, crusts
Hardness: 4.5
Specific gravity: 3.57 to 3.79
Cleavage: 1; {010} imperfect
Tenacity:
Streak:
Synonyms/varieties:
Comments: crystals zoned: center colourless, exterior red, reddish brown, dark brown or black
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