| Orpiment | |
|---|---|
 Orpiment crystal from Twin Creeks Mine, Potosi District, Humboldt County, Nevada, United States (Size: 3.3 cm × 2.1 cm × 2.1 cm) | |
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | As2S3 |
| IMA symbol | Orp[1] |
| Strunz classification | 2.FA.30 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/n |
| Unit cell | a = 11.475(5), b = 9.577(4) c = 4.256(2) [Å], β = 90.45(5)°; Z = 4 |
| Identification | |
| Color | Lemon-yellow to golden or brownish yellow |
| Crystal 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}; |
| Tenacity | Sectile |
| Mohs scale hardness | 1.5–2 |
| Luster | Resinous, pearly on cleavage surface |
| Streak | Pale lemon-yellow |
| Diaphaneity | Transparent |
| Specific gravity | 3.49 |
| Optical properties | Biaxial (−) |
| Refractive index | 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 angle | Measured: 30° to 76°, Calculated: 62° |
| Dispersion | r > v, strong |
| References | [2][3][4] |
Orpiment, also known as ″yellow arsenic blende″ is a deep-colored, orange-yellow arsenic sulfide mineral with formula As
2S
3. 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.
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Orpiment" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 14 March 2022.
- ^ Orpiment, Mindat.org, retrieved 26 May 2022
- ^ Orpiment, WebMineral.com, retrieved 26 May 2022