Formula: [](Fe,Mg)7Si8O22(OH)2
Origin of name: For E. Louis Grüner, French chemist
Crystal system: Monoclinic
Crystal class: 2/m
Twinning:
Unit cell:
Colour: Ash gray, dark green, brown
Diaphaneity: Translucent to nearly opaque
Luster: Silky
Habit: Fibrous or fibrolamellar, often in radiating clusters
Hardness: 5 to 6
Specific gravity: 3.44 to 3.60
Cleavage: 1; {110} good
Tenacity:
Streak:
Synonyms/varieties:
Comments: Series with cummingtonite and with manganogrunerite
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