Formula: (Fe,Mn)(Ta,Nb)2O6
Origin of name: for Tapio, a Finnish god
Crystal system: Tetragonal
Crystal class: 4/m 2/m 2/m
Twinning: polysynthetic and simple twinning
Unit cell: a = 4.754, c = 9.228
Colour: Black
Diaphaneity: Opaque
Luster: Submetallic to subadamantine
Habit: Crystals short prismatic or equant, often distorted appearing monoclinic or orthorhombic, polysynthetic and simple twinning
Hardness: 6 to 6.5
Specific gravity: 8.17
Cleavage: {110} imperfect
Tenacity: Uneven fracture
Streak: Blackish brown to brownish gray, brown
Synonyms/varieties:
Comments: dimorphous with ferrotantalite, see also the end-members of the tapiolite series: ferrotapiolite and manganotapiolite
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