Orpiment

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
CategorySulfide mineral
Formula
(repeating unit)
As2S3
IMA symbolOrp[1]
Strunz classification2.FA.30
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/n
Unit cella = 11.475(5), b = 9.577(4)
c = 4.256(2) [Å], β = 90.45(5)°; Z = 4
Identification
ColorLemon-yellow to golden or brownish yellow
Crystal habitCommonly in foliated columnar or fibrous aggregates; may be reniform or botryoidal; also granular or powdery; rarely as prismatic crystals
TwinningOn {100}
CleavagePerfect on {010}, imperfect on {100};
TenacitySectile
Mohs scale hardness1.5–2
LusterResinous, pearly on cleavage surface
StreakPale lemon-yellow
DiaphaneityTransparent
Specific gravity3.49
Optical propertiesBiaxial (−)
Refractive indexnα = 2.400 nβ = 2.810 nγ = 3.020
Birefringenceδ = 0.620
PleochroismIn reflected light, strong, white to pale gray with reddish tint; in transmitted light, Y = yellow, Z = greenish yellow
2V angleMeasured: 30° to 76°, Calculated: 62°
Dispersionr > 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
2
S
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.

  1. ^ 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.
  2. ^ 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.
  3. ^ Orpiment, Mindat.org, retrieved 26 May 2022
  4. ^ Orpiment, WebMineral.com, retrieved 26 May 2022