Table of Contents
Orpiment is a soft yellow or orange mineral. Widely distributed, it is typically powdery or massive, but it is also found as cleavable, columnar, or foliated masses. Distinct crystals are uncommon, but when found they are short prisms. Orpiment occurs in hydrothermal veins at Iow temperature (up to 400°F/ 200°C), hot spring deposits, and volcanic fumaroles, and it may occur with stibnite and realgar. It also results from the alteration of other arsenic-bearing minerals. When heated, orpiment gives off the garlic odor typical of arsenic minerals. The luster is resinous on freshly broken surfaces but pearly on cleavage surfaces. It was used as a pigment, mainly in ancient times in the Middle East. It was also used later in the West but soon replaced due to its toxicity
Name: From the Latin auripigmentum, golden paint, in allusion to the color.
Chemistry: Stated to be very near As2S3.
Cell Data: Space Group: P21/n. a = 11.475(5) b = 9.577(4) c = 4.256(2) β = 90◦41(5)0 Z=4
X-ray Powder Pattern: Baia Sprie (Fels˝ob´anya), Romania. 4.85 (100), 4.02 (50), 2.47 (40), 1.755 (40), 3.22 (30), 2.79 (30), 2.72 (30)
Association: Stibnite, realgar, arsenic, calcite, barite, gypsum.
Crystallography: Monoclinic; prismatic. Crystals small, tabular or short prismatic, and rarely distinct. Usually in foliated or columnar masses
Composition: Arsenic trisulfide, AS2S3 . As = 61. percent, S = 39 percent.
Chemical Properties of Orpiment
| Chemical Classification | Sulfide mineral |
| Chemical Composition | As2S3 |
Physical Properties of Orpiment
| Color | Lemon-yellow to golden or brownish yellow |
| Streak | Pale lemon-yellow |
| Luster | Resinous, pearly on cleavage surface |
| Cleavage | Perfect Perfect {010} imperfect {100} |
| Diaphaneity | Transparent |
| Mohs Hardness | 1.5 – 2 |
| Crystal System | Monoclinic |
| Tenacity | Sectile |
| Density | 3.49 |
Optical Properties of Orpiment
| Type | Anisotropic |
| Color / Pleochroism | Strong |
| 2V: | Measured: 30° to 76°, Calculated: 62° |
| RI values: | nα = 2.400 nβ = 2.810 nγ = 3.020 |
| Twinning | On {100} |
| Optic Sign | Biaxial (-) |
| Birefringence | δ = 0.620 |
| Relief | Very High |
| Dispersion: | relatively strong r > v |
Occurrence
Realgar and orpiment are especially discovered related to hydrothermal and volcanic activities. They are sublimation merchandise at volcanic vents and crystallization products at warm springs. These are the various earliest deposits exploited in the middle a while. Underground deposits of realgar and orpiment are in veins and fractures. There they may be related to lead, silver, gold, and different arsenic minerals.
Uses Area
Used in dyeing and in a preparation for the removal of hair from skins. Artificial arsenic sulfide is largely used in place of the mineral. Formerly both realgar and orpiment were used as pigments but are no longer because of their poisonous nature.
Distribution
Not uncommon in small amounts, but rare in fine specimens.
- In the USA, crystallized from Mercur, Tooele Co., Utah; in Nevada, at the Getchell mine, Humboldt Co.; from the White Caps mine, Manhattan, Nye Co.; with fine examples from in the Twin Creeks mine, Humboldt Co.
- At Tajov, Slovakia.
- From Kresevo, Bosnia-Herzegovina.
- At Alsar (Allchar), near Rosden, Macedonia.
- Fine crystals from the Zarshuran gold deposit, 35 km north of Takab, northwestern Iran.
- From Turkey.
- In Russia, at Loukhoumi, Caucasus Mountains, and Men-Kyule, Sakha.
- From Racha Luyumi, Georgia.
- Large crystals from the Shimen mine, 33 km southeast of Shimen, Hunan Province, China.
- Exceptional specimens from the Quiruvilca mine, La Libertad, Peru.
References
- Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
- Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
- Mindat.org. (2019). Orpiment: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
- Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].
