Orpiment

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Orpiment
Orpiment, réalgar, barytine, calcite 300.4.FS2014.jpg
General
CategorySulfide mineral
Formula
(repeating unit)
As2S3
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[1][2][3]

Orpiment is a deep orange-yellow colored arsenic sulfide mineral with formula As
2
S
3
. It is found in volcanic fumaroles, low temperature hydrothermal veins, and hot springs and is formed both by sublimation and as a byproduct of the decay of another arsenic mineral, realgar. It takes its name from the Latin auripigmentum (aurum − gold + pigmentumpigment) because of its deep-yellow color.

Historical uses[edit]

Bright goldenyellow streak colour of orpiment

Orpiment was traded in the Roman Empire and was used as a medicine in China even though it is very toxic. It has been used as a fly poison and to tip arrows with poison.[citation needed] Because of its striking color, it was of interest to alchemists, both in China and the West, searching for a way to make gold.

For centuries, orpiment was ground down and used as a pigment in painting and for sealing wax, and is even used in Ancient China as a correction fluid.[4] It was one of the few clear, bright-yellow pigments available to artists until the 19th century. However, its extreme toxicity and incompatibility with other common pigments, including lead and copper-based substances such as verdigris and azurite,[5] meant that its use as a pigment ended when cadmium yellows, chromium yellows and organic dye-based colors were introduced during the 19th century.

Orpiment, as the Latin Auripigmentum, is mentioned by Robert Hooke in Micrographia for the manufacture of small shot in the 17th century.[6]

Contemporary uses[edit]

Orpiment is used in the production of infrared-transmitting glass, oil cloth, linoleum, semiconductors, photoconductors, pigments, and fireworks. Mixed with two parts of slaked lime, orpiment is still commonly used in rural India as a depilatory. It is used in the tanning industry to remove hair from hides.

Physical and optical properties[edit]

Orpiment is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.49. It melts at 300 °C to 325 °C. Optically it is biaxial (−) with refractive indices of a = 2.4, b = 2.81, g = 3.02.

Crystal structure[edit]

Gallery of orpiment specimens[edit]

See also[edit]

References[edit]

  1. ^ Handbook of Mineralogy
  2. ^ Mindat.org
  3. ^ Webmineral data
  4. ^ [dead link][1]
  5. ^ Fitzhugh, E.W., Orpiment and Realgar, in Artists’ Pigments, A Handbook of Their History and Characteristics, Vol 3: E.W. Fitzhugh (Ed.) Oxford University Press 1997, p. 52
  6. ^ Hooke, Robert. "Micrographia". Project Gutenberg. Retrieved 24 October 2012.
  • The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. 11th Edition. Ed. Susan Budavari. Merck & Co., Inc., N.J., U.S.A. 1989.
  • William Mesny. Mesny’s Chinese Miscellany. A Text Book of Notes on China and the Chinese. Shanghai. Vol. III, (1899), p. 251; Vol. IV, (1905), pp. 26.
  • Fitzhugh, E.W., Orpiment and Realgar, in Artists’ Pigments, A Handbook of Their History and Characteristics, Vol 3: E.W. Fitzhugh (Ed.) Oxford University Press 1997, p. 47 – 80

External links[edit]