Kermesite

Chemical Formula: Sb₂S₂O
Locality: Braunsdorf, near Freiberg, Saxony, Germany.
Name Origin: Name from kermes, a name given from the Persian qurmizq, “crimson” in the older chemistry to red amorphous antimony trisulphide, often mixed with antimony trioxide.Kermesite or antimony oxysulfide is also known as red antimony (Sb₂S₂O) . The mineral’s color ranges from cherry red to a dark red to a black. Kermesite is the result of partial oxidation between stibnite (Sb₂S₃)) and other antimony oxides such as valentinite (Sb₂O₃) or stibiconite (Sb₃O₆(OH)). Under certain conditions with oxygenated fluids the transformation of all sulfur to oxygen would occur but kermesite occurs when that transformation is halted.

Physical Properties

Cleavage: {100} Perfect
Color: Violet red, Cherry red, Red.
Density: 4.5 – 4.6, Average = 4.55
Diaphaneity: Translucent to Opaque
Fracture: Brittle – Generally displayed by glasses and most non-metallic minerals.
Hardness: 1.5-2 – Talc-Gypsum
Luminescence: Non-fluorescent.
Luster: Adamantine
Magnetism: Nonmagnetic
Streak: brownish red

Photos: