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Formula: AsS
Simple sulphide of arsenic
Crystal System: Monoclinic
Specific gravity: 3.56 measured, 3.59 calculated
Hardness: 1½
Streak: Orange yellow
Colour: Deep red to orange
Solubility: Slightly soluble in nitric acid
Environments:
Sedimentary environments
Volcanic sublimates and hot spring deposits
Hydrothermal environments
(typical)
Realgar is a common epithermal (low temperature) hydrothermal vein mineral in
veins of lead, silver and
gold ores associated with
orpiment, arsenolite, other
arsenic minerals,
calcite, baryte and
stibnite.
It also occurs as a volcanic sublimation product associated with sulphur, as a deposit in
hot springs, and in carbonate sedimentary rocks
(HOM, Dana, MOM).
Realgar decomposes to pararealgar with exposure to light, and decays to form
orpiment.
Localities
At Llallagua, Rafael Bustillo, Potosí, Bolivia, microcrystals of realgar are occasionally seen coating
arsenopyrite, and one mass of native arsenic
and gypsum shows lamellae of realgar
(Minrec 37.2.151).
At Jiepaiyu Mine, Shimen deposit, Shimen county, Changde, Hunan, China, realgar is the principal ore mineral, and
calcite is the main gangue mineral
(Minrec 38.1.52).
Realgar from the Jiepaiyu Mine -
Image
At the Bouismas Mine, Zagora Province, Drâa-Tafilalet Region, Morocco, realgar crystals to 2 mm on
calcite have been found in a löllingite vein
(Minrec 38.5.389).
Realgar from the Bouismas Mine -
Image
At the Palomo Mines, Huachocolpa District, Huancavelica Province, Huancavelica, Peru, very dark red crystals realgarto 4 cm on
quartz druses have been found (Minrec 42.2.166), partially altered to
pararealgar. A few specimens of realgar to 1 cm have been found with
tetrahedrite, galena and
sphalerite
(Minrec 39.2.99).
Realgar from the Palomo Mines - Image
At Baia Sprie mine, Baia Sprie, Maramureș, Romania, fine crystals realgar to 6 cm on a chalky white matrix with
quartz and pyrite. some show mixtures of
realgar and stibnite crystals overlying realgar of an earlier
generation
(Minrec 37.3.243-244).
Realgar from Baia Sprie - Image
At White Caps Mine, Manhattan, Manhattan Mining District, Toquima Range, Nye county, Nevada, USA, acicular crystals of
picropharmacolite typically occur on a druse of realgar
(Minrec 41.6.547)
Realgar from White Caps Mine - Image
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