Realgar & pararealgar & calcite on marble Realgar, Royal Reward Mine, Green River Gorge, Franklin, King County, Washington, USA Realgar, Royal Reward Mine, Green River Gorge, Franklin, King County, Washington, USA
Realgar is a member of sulfide mineral with chemical composition is As4S4 or AsS. It is bright red or orange in color. Crystals are not often found, but when they occur they are short, prismatic, and striated. Realgar mostly occurs as coarse to fine granular masses and as encrustations. Realgar disintegrates on prolonged exposure to light, forming an opaque yellow powder, which is principally pararealgar. Therefore, specimens are kept in darkened containers. Realgar is typically found in hydrothermal deposits at low temperature (up to 400°F/200°C) often with orpiment and other arsenic minerals. It also forms as a sublimate around volcanoes, hot springs, and geyser deposits and as a weathering product of other arsenic-bearing minerals. Realgar is often found with stibnite and calcite.
Polymorphism & Series: Trimorphous with alacr´anite and pararealgar
Name: From the Arabic rahj al ghar for powder of the mine
Association: Orpiment, arsenolite, other arsenic minerals, calcite, barite
Crystallography: Monoclinic; prismatic. Found in short, vertically striated, prismatic crystals. Frequently coarse to fine granular and often earthy and as an incrustation.
Composition: Arsenic monosulfide, AsS. As = 70.1 percent, S = 29.9 percent.
Diagnostic Features: Realgar can be distinguished by its red color, resinous luster, and almost invariable association with orpiment. Its orange-red streak serves to distinguish it from other red minerals
Chemical Properties of Realgar
Chemical Classification | Sulfide mineral |
Chemical Composition | As4S4 or AsS |
Physical Properties of Realgar
Color | Red to yellow-orange; in polished section, pale gray, with abundant yellow to red internal reflections |
Streak | Red-orange to red |
Luster | Resinous to greasy |
Cleavage | Good on {010}; less so on {101}, {100}, {120}, and {110} |
Diaphaneity | Transparent |
Mohs Hardness | 1.5–2 |
Specific Gravity | 3.56 |
Diagnostic Properties | Toxic and carcinogenic. Disintegrates on long exposure to light to a powder composed of pararealgar or arsenolite and orpiment. |
Crystal System | Monoclinic |
Tenacity | Sectile |
Density | 3.56 g/cm3 (Measured) 3.59 g/cm3 (Calculated) |
Optical Properties of Realgar

Type | Anisotropic |
Color / Pleochroism | Nearly colorless to pale golden yellow |
Twinning | Contact twins on {100} |
Optic Sign | Biaxial (-) |
Birefringence | δ = 0.166 |
Relief | Very High |
Occurrence
Realgar is found in veins of lead, silver, and gold ores associated with orpiment, other arsenic minerals, and stibnite. It also occurs as a volcanic sublimation product and as a deposit from hot springs
Uses Area
- An ore of arsenic.
- Historically used as a pigment
- Depilatory
- Poison
- Ingredient in explosives and fireworks
- Ritualistic “medicine,” cosmetic.
Distribution
Only localities for finely crystallized material are given.
- In Germany, from Schneeberg, Saxony, and at St. Andreasberg, Harz Mountains.
- In the Lengenbach quarry, Binntal, Valais, Switzerland.
- In Romania, from Baia Sprie , Cavnic (Kapnikbanya), and at Sacarımb (Nagyag).
- In the Czech Republic, from Jachymov (Joachimsthal).
- At Alsar (Allchar), near Rosden, Macedonia.
- From Men-Kyule, Sakha, Russia.
- At Saimoku, Prefecture, Japan.
- In the Shimen mine, 33 km southeast of Shimen, Hunan Province, China. In the USA, fine large crystals at the Getchell mine, Potosi district, Humboldt Co., Nevada; in Tooele Co., Utah, at Mercur; in Washington, in the Monte Cristo district, Snohomish Co., and in the Royal Reward mine, in the Green River Gorge, King Co.
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). Realgar: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/min-727.html [Accessed 4 Mar. 2019].