Formula: Pb(Sb,As)2S4
Origin of name: for R. Thompson, Canadian mineralogist (Thompson = son of Thomas, Thomas in Aramaic = twin)
Crystal system: orthorhombic
Crystal class: unknown
Twinning: polysynthetic
Unit cell:
Colour: black
Diaphaneity: opaque
Luster: metallic
Habit: six grains known, two to 1.5 mm, 4 microscopic, polysynthetic twinning
Hardness: 3.5
Specific gravity: 5.26
Cleavage: 1; {100} perfect
Tenacity:
Streak: black with slight brownish tint
Synonyms/varieties:
Comments: dimorphous with guettardite
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