Formula: (Pb,Sn)6FeSn2Sb2S14
Origin of name: For C. and E. Francke, mining engineers, Bolivia
Crystal system: Triclinic
Crystal class: -1
Twinning:
Unit cell:
Colour: Grayish black
Diaphaneity: Opaque
Luster: Metallic
Habit: Crystals thin tabular, somewhat elongated, vertically striated; in spherical aggregates; massive, foliated or radial
Hardness: 2.5 to 3
Specific gravity: 5.88 to 5.92
Cleavage: 1; {001} perfect
Tenacity:
Streak: Grayish black
Synonyms/varieties:
Comments:
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