Sulfides: Arsenopyrite

Composition: FeAsS; cobalt may substitute for iron

Crystal system: Orthorhombic; typically well crystallized

7.1.1
crystalline arsenopyrite
Biggenden mine Qld Australia

Properties:

• Metallic lustre
• Silver grey
• Dark streak (grey to black)
• Knife barely scratches or not at all (Mohs Hardness 5.5-6)
• High density
• Two cleavages at 68o sometimes apparent
• Uneven fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Arsenopyrite, the most common arsenic mineral, occurs with other sulfides in hydrothermal vein and replacement ore deposits. It is found mainly in hydrothermal gold, tin and tungsten deposits.

7.1.2
crystalline arsenopyrite
Biggenden mine Qld Australia

Arsenopyrite is not mined for its arsenic content; however, arsenic is a byproduct of the smelting of ores containing arsenopyrite. Arsenic emissions from historic smelting of such ores has resulted in contamination of the surrounding areas. Modern smelters do not accept such ores or are specially equipped to recover the arsenic for industrial use such as insecticides.