Orpiment is a mineral of arsenic sulfide with a deep yellow-orange color, occurring in hydrothermal veins of low temperature, volcanic fumaroles, and in hot springs as well. Its formation occurs from the decay of Realgar, another mineral belonging to the arsenic group or by sublimation. Its name derives from Latin’s Auripigmentum, (aurm meaning gold and pigmentum referring to pigment).
Derivation of Name
The name "Orpiment" is derived from Latin auripigmentum, a pointer to the vibrant golden hue. Orpiment, as the Latin Auripigmentum, is referred to by Robert Hooke in Micrographia for manufacturing small shot in the seventeenth century.
It's a sulfide of arsenic, which is widespread in nature, but has comparatively small deposits. Using modern technology its artificial version can be created through a process of sublimation and precipitation. It possesses a rich lemon or canary yellow color with fair covering power and good chemical stability.
Orpiment has photosensitive, arresting gem-like crystals. It should not be exposed to direct sunlight and must be stored in dry, light proof containers.
It’s mainly found in Peru; Romania; Mercury, USA; Utah, Japan and Australia.
Orpiment is an uncommon mineral that generally gets formed with Realgar. Actually, the two minerals are just about always together. Crystals of orpiment are awfully rare as it regularly forms masses and crusts. At times, the masses are transparent to an extent and have a gem-like quality about them. Its unusual yellow color may be confused with not many other minerals. Because of its instability, its utility as a pigment or dye is limited. Ultimately, orpiment deteriorates into a powder. Though the process is extremely time consuming, exposure to light accelerates it.
Color varies from orange-yellow to yellow.
Mohs scale hardness
1.5 - 2