Olmsteadite

Formula: KFe2(Nb,Ta)(PO4)2O2.2H2O

Origin of name: for Milo Olmstead, American micromounter

 

Crystal system: orthorhombic

Crystal class: mm2

Twinning: 

Unit cell: a = 7.478 Å, b = 10.04 Å, c = 80531 Å

 

Colour: deep brown to black

Diaphaneity: 

Luster: subadamantine

Habit: crystals thin to thick tabular, smaller than 1 mm

Hardness: 4

Specific gravity: 3.36

Cleavage: 2; {100} and {001} good

Tenacity: 

Streak: olive green

 

Synonyms/varieties:

 

Comments: 

 

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