Orpiment

Orpiment
Orpiment
General
Category	Sulfide mineral
Formula; (repeating unit)	As2S3
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

Orpiment 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 is formed both by sublimation and as a byproduct of the decay of another arsenic mineral, realgar. Orpiment takes its name from the Latin auripigmentum (aurum, "gold" + pigmentum, "pigment") because of its deep-yellow color.

Historical uses[]

Bright golden-yellow streak color 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 fly poison^[4] and to tip arrows with poison.^[5] Because of its striking color, it was of interest to alchemists, both in China and the West, searching for a way to make gold. It also has been found in the wall decorations of Tutankhamun's tomb and ancient Egyptian scrolls, and on the walls of the Taj Mahal.^[6]

For centuries, orpiment was ground down and used as a pigment in painting and for sealing wax, and was even used in ancient China as a correction fluid.^[7] 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,^[8]^[6] 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 is mentioned in the 17th century by Robert Hooke in Micrographia for the manufacture of small shot.^[9]

Contemporary uses[]

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[]

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 (570 °F) to 325 °C (620 °F). Optically, it is biaxial (−) with refractive indices of a = 2.4, b = 2.81, g = 3.02.

Crystal structure[]

Orpiment's unit cell
Orpiment's crystal structure consists of sheets
The sheets are stacked into layers

Gallery of orpiment specimens[]

Orpiment and realgar on a vuggy, quartz matrix, Nishinomaki Mine, Gunma Prefecture, Japan
Orpiment from La Libertad, Quiruvilca, Peru
El'brusskiy arsenic mine, Kabardino-Balkarian Republic, Northern Caucasus Region, Russia
Orpiment crystal from Twin Creeks Mine, Potosi District, Humboldt County, Nevada, United States

References[]

^ Handbook of Mineralogy
^ Mindat.org
^ Webmineral data
^ Miller, George (1826). Popular philosophy: or, The book of nature laid open upon Christian principles, by the ed. of The Cheap magazine.
^ Mesny, William (1899). Mesny's Chinese Miscellany. China Gazette Office.
^ ^a ^b St. Clair, Kassia (2016). The Secret Lives of Colour. London: John Murray. pp. 82–83. ISBN 9781473630819. OCLC 936144129.
^ ^{[dead link]}[1]
^ 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
^ 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[]

Webexhibits "Pigments Through the Ages: Orpiment"
Babylonian Talmud Tractate Chullin see Rashi 'haZarnich' (in Hebrew)
Orpiment, Colourlex

[Handbook-1] Handbook of Mineralogy

[Mindat-2] Mindat.org

[Webmin-3] Webmineral data

[4] Miller, George (1826). Popular philosophy: or, The book of nature laid open upon Christian principles, by the ed. of The Cheap magazine.

[5] Mesny, William (1899). Mesny's Chinese Miscellany. China Gazette Office.

[StClair-6] St. Clair, Kassia (2016). The Secret Lives of Colour. London: John Murray. pp. 82–83. ISBN 9781473630819. OCLC 936144129.

[7] {[dead link]}[1]

[8] 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

[9] Hooke, Robert. "Micrographia". Project Gutenberg. Retrieved 24 October 2012.

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