Formula: (Mg,Mn)2(Mn,Fe)BO5
Origin of name: for Yoshio Takéuchi (1924-), Japanese mineralogist
Crystal system: Orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell: a = 27.5, b = 12.614, c = 6.046
Colour: Black
Diaphaneity: Opaque
Luster: Metallic
Habit: Crystals acicular, to 10 mm, with rhombohedral cross section perpendicular to the dominant form {320}
Hardness: 6
Specific gravity: 3.93
Cleavage: None
Tenacity: Uneven fracture
Streak: Brown
Synonyms/varieties:
Comments: polymorphous with fredrikssonite, orthopinakiolite and pinakiolite
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