Formula: (Fe,Mg)2FeO2(BO3)
Origin of name: for M. Vonsen, American collector
Crystal system: orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell:
Colour: black
Diaphaneity: opaque
Luster: submetallic to adamantine
Habit: crystals stubby prisms, diamond-shaped cross sections, uncommon, granular polygonal aggregates
Hardness: 5
Specific gravity: 4.77
Cleavage: none
Tenacity:
Streak:
Synonyms/varieties:
Comments: series with ludwigite
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