Formula: MnO(OH)
Origin of name: For Frank Grout, American petrologist
Crystal system: Orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning: Noted
Unit cell: a = 4.565 Ǻ, b = 10.70 Ǻ, c = 2.852 Ǻ
Colour: Jet black
Diaphaneity:
Luster: Brilliant submetallic to adamantine
Habit: Crystals wedge- or lens-shaped with rounded faces, or slender prismatic
Hardness: ~ 5.5
Specific gravity: 4.14
Cleavage: 2; {010} perfect, {100} distinct
Tenacity: Uneven; brittle
Streak: Dark brown
Synonyms/varieties:
Comments: Trimorphous with manganite and feitknechtite
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