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Realgar 

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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

Realgar optical PPL and XPL
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].
Cite this article as: Geology Science. (2019). Realgar . [online] Available at: http://geologyscience.com/minerals/realgar/ [15th September 2019 ]
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