Description
The mineral orpiment, or auripigment, is an arsenic sulfide with the chemical formula As2S3. The transparent to translucent lemon-yellow, orange-yellow, or brown-yellow orpiment has a pearlescent luster, pale yellow streaks, and perfect cleavage along the crystal plane [010]. The crystal system is monoclinic. Orpiment has an average density of 3.52, a hardness of 1.5 to 2, and is not radioactive. The mineral is strongly pleochroic, ranging from white to grayish-white with a light red tinge. The name of the mineral auripigment is derived from the Latin aurus (gold) and pigmentum (dye), due to the mineral's golden sheen. As a yellow dye, it was also known as operment, yellow sulfur arsenic, Russian yellow, Chinese yellow, or king's yellow. Orpiment is a mineral formed in low-temperature hydrothermal veins, in hot springs, and as a weathering product of arsenic-bearing minerals, primarily realgar. The type locality has not been determined. The mineral is found, among other places, in the Twin Creeks mine, north of Winnemucca, Humboldt County, Nevada, United States.
