arsenopyrite

Arsenopyrite is an iron arsenic sulfide mineral with the chemical formula FeAsS. It is one of the most common arsenic-bearing minerals and occurs widely in hydrothermal veins, high-temperature metamorphic zones, and some igneous rocks. It is notably associated with gold mineralization in quartz-vein deposits.

Arsenopyrite has a metallic luster and a steel-gray to tin-white color, often with a brass-yellow cast on fresh surfaces. Crystals are typically elongated prismatic in the tetragonal system, though it commonly appears as coarse masses. It has a Mohs hardness of 5.5–6 and a density around 5.9–6.2 g/cm3. The streak is gray to dark gray, and cleavage is indistinct with uneven fracture. On exposure to air, it can tarnish to a dull gray, olive, or yellowish patina.

Formation and associations: It forms in high-temperature hydrothermal ore veins and is commonly found with quartz, calcite, pyrite, sphalerite, galena, and stibnite. It is often encountered in gold-bearing deposits and can occur in contact metamorphic rocks as well.

Economic and safety notes: Arsenopyrite is an important source of arsenic; roasting it yields arsenic trioxide. It can also provide iron and arsenic as byproducts. Due to its arsenic content, handling and processing pose health and environmental hazards, requiring appropriate safety measures and waste management in mining and processing operations.