Formula: (Fe,Mn)Fe4(PO4)3(OH)5
Origin of name: after locality Rockbridge County, Virginia, USA
Crystal system: orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell: a = 13.78 Å, b = 16.81 Å, c = 5.172 Å
Colour: olive-green to nearly black, brownish green to reddish brown
Diaphaneity:
Luster: vitreous to dull
Habit: crystals slender prismatic, minute, singles or radial aggregates, botryoidal crusts, massive, radial fibrous to columnar
Hardness: 4.5
Specific gravity: 3.3 to 3.49
Cleavage: 3; {100} perfect, {010} and {001} distinct
Tenacity: uneven, brittle
Streak:
Synonyms/varieties:
Comments: series with frondelite
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