ORPIMENT (from the Latin words "aurum" (gold) and "pigmentum" (pigment) * EN: orpiment, yellow arsenic; DE: Auripigment; FR: auripigment, orpiment; ES: oropimente; RU: аурипигмент) is the mineral of the class of sulfides, As2S3. Sometimes it contains the impurity of Sb (up to 3%). It crystallizes into the monoclinic crystal system. The crystal structure is layered, is built of the complicated corrugated layers, which have been formed by the chained AsS3 groups. The form of the isolations is: radiant-radiating intergrowths with the comb-like surface, and also the spherulites, dense or earthy masses, incrustations, crusts. The crystals are rare. The colour is from the lemon-yellow and golden-yellow to orange-yellow. It is translucent. The cleavage is very perfect. The hardness is 1.5-2. The density is 3500 kilograms per cubic metre. It is diamagnetic.

Orpiment is the typical mineral of the medium-temperature and low-temperature arsenic and antimony-mercury deposits (for example, Khaidarkan, within Kyrgyzstan). Large deposits of orpiment are known since the ancient times within the Yugoslavia (Macedonia) and Iran (Kurdistan). Orpiment may be found also within the Switzerland (Binnental), West Germany (Saint Andreasberg), Romania, China (Xiaguan, within the Yunnan province), USA (Mercur, within the Utah state), and other places. Orpiment in association with realgar forms itself within the sublimates of Vesuvius and volcanos of Java. It is known also within the depositions of the thermal water sources (Kuriyama, within Japan; Kamchatka, within the USSR; Yellowstone Park, within the USA). During the weathering, it transitions into the arsenolite, As2O3.

Orpiment was used as the yellow paint since the antiquity. They use in within the laquer-paint and leather industries. At the certain deposits, orpiment (together with realgar) is mined as the arsenic ores. The major method of beneficiation is flotation. The collectors are the neutral hydrocarbon oils, xanthates after the activation by the copper(II) sulfate pentahydrate with the narrow interval of the consumption of the latter, shale resin with the foaming agent, namely, pine oil.