orpiment

{{infobox mineral | name = Orpiment | category = Sulfide mineral | boxwidth = | boxbgcolor = | image = Orpiment-148270.jpg | imagesize = | alt = | caption = Orpiment crystal from Twin Creeks Mine, Potosi District, Humboldt County, Nevada, United States (Size: 3.3 cm × 2.1 cm × 2.1 cm) | formula = As2S3 | IMAsymbol = Orp | molweight = | strunz = 2.FA.30 | dana = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/n | unit cell = a = 11.475(5), b = 9.577(4) c = 4.256(2) [Å], β = 90.45(5)°; Z = 4 | color = Lemon-yellow to golden or brownish yellow | colour = | habit = Commonly in foliated columnar or fibrous aggregates; may be reniform or botryoidal; also granular or powdery; rarely as prismatic crystals | twinning = On {100} | cleavage = Perfect on {010}, imperfect on {100}; | fracture = | tenacity = Sectile | mohs = 1.5–2 | luster = Resinous, pearly on cleavage surface | streak = Pale lemon-yellow | diaphaneity = Transparent | gravity = 3.49 | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 2.400 nβ = 2.810 nγ = 3.020 | birefringence = δ = 0.620 | pleochroism = In reflected light, strong, white to pale gray with reddish tint; in transmitted light, Y = yellow, Z = greenish yellow | 2V = Measured: 30° to 76°, Calculated: 62° | dispersion = r > v, strong | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} Orpiment, also known as yellow arsenic blende, is a deep-colored, orange-yellow arsenic sulfide mineral with formula . It is found in volcanic fumaroles, low-temperature hydrothermal veins, and hot springs and may be formed through sublimation.

Orpiment takes its name from the Latin auripigmentum (aurum, "gold" + pigmentum, "pigment"), due to its deep-yellow color. Orpiment once was widely used in artworks, medicine, and other applications. Because of its toxicity and instability, its usage has declined.