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 | [1][2][3] |
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
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
See also
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
