Orpiment
Orpiment | |
---|---|
![]() Orpiment
|
|
General | |
Category | Sulfide mineral |
Formula (repeating unit) |
As2S3 |
Strunz classification | 02.FA.30 |
Crystal symmetry | Monoclinic 2/m |
Unit cell | a = 11.475(5) Å, b = 9.577(4) Å, 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 |
Crystal system | Monoclinic Prismatic |
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 | [1][2][3] |
Orpiment is a deep orange-yellow colored arsenic sulfide mineral with formula As2S3. 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 + pigmentum − pigment) because of its deep-yellow color.
Contents
Historical uses[edit]
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. 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. 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,[4] 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.[5]
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]
-
Orpiment's unit cell -
Orpiment's crystal structure consists of sheets
Gallery of orpiment specimens[edit]
-
Orpiment and realgar on a vuggy, quartz matrix, Nishinomaki Mine, Gunma Prefecture, Japan. Size: 5.5 x 4.0 x 3.8 cm.
-
El'brusskiy arsenic mine, Kabardino-Balkarian Republic, Northern Caucasus Region, Russia. Size 5.8 x 3.5 x 1.7 cm.
References[edit]
- ^ http://rruff.geo.arizona.edu/doclib/hom/orpiment.pdf Handbook of Mineralogy
- ^ http://www.mindat.org/min-3021.html Mindat.org
- ^ http://webmineral.com/data/Orpiment.shtml Webmineral data
- ^ 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[edit]
- Webexhibits "Pigments Through the Ages: Orpiment"
- Babylonian Talmud Tractate Chullin see Rashi 'haZarnich' (Hebrew)
- Orpiment, Colourlex
![]() |
Wikimedia Commons has media related to Orpiment. |