Get to Know a Mineral: Realgar!

And now for another installment of "Get to know a Mineral!"  It's been a while, but I thought I'd write about a mineral I found not too long ago on my job site: Realgar!

Realgar, or "ruby sulphur" as it is sometimes called, is an arsenic sulfide mineral (As₄S₄).  As its moniker suggests, it is red in colour but is also known to be orange.   It is a soft mineral (1.5 to 2 on the Mohs Scale of Hardness) that occurs in monoclinic crystals or as powder.  It is often associated with orpiment (As₂S₃), as well as calcite and barite.

Its etymological beginnings originate from Arabic: رهج الغار, meaning 'powder of the mine'.  Realgar was called "sandaracha" by the ancient Greeks who knew of its poisonous nature.  This nature was exemplified when realgar was used to poison rats in medieval Spain and in sixteenth-century England.  It was a prominent item of trade in the ancient Roman Empire, where it was used for red paint and as a medicine.  China also utilized it as a medicine, incorporating it into household items such as wine cups, images and charms in the hope that it would ward off disease.

Commonly occurring as a low-temperature hydrothermal vein mineral associated with other arsenic and antimony minerals, realgar also comes about from volcanic sublimations and in hot spring deposits.  Well known localities include China, Switzerland, Turkey and Peru.  Realgar occurs with lead, silver and gold ores in Hungary, Bohemia and Saxony.  The United States also boasts mines with realgar occurences, as well as in the geyser deposits of Yellowstone National Park.

In years past, realgar was used to perform corrosive work in industries such as leather manufacturing, where it would be used to remove the hair from animal pelts. The use of its corrosive nature has been abandoned in modern times due to its listing as a known carcinogen, and because cheaper competing products exist.  It is however, still sometimes used in the killing of weeds, insects, and rodents.

For a geologist, realgar is an exciting indicator mineral and a favorite of mineral collectors.  It has been known to change to a yellow powdery form after being subjected to long periods of light.  This yellow powder was once thought to be orpiment, however it has recently been shown to possess a distinct chemical compound and is known as pararealgar.

Also Get to Know:

Molybdenite
Garnet
Cummingtonite

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