Realgar

Realgar is an arsenic sulfide mineral with formula: As₄S₄. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment (As₂S₃). It is orange-red in colour, melts at 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur. Realgar is soft with a Mohs hardness of 1.5 to 2 and has a specific gravity of 3.5.

Its name comes from Arabic rahj al-ghār – 'powder of the mine,' via Catalonian, Middle Latin, and Middle English. In India Realgar is known as manseel, and orpiment as hartal.

It was, along with orpiment, a significant item of trade in the ancient Roman Empire and was used as a pigment and a medicine. It was also used as a medicine in China and "is made up into household ornaments, such as wine pots, wine cups, images, paperweights, and various other kinds of ornamanets and charms, to be kept near at hand in use, or worn about the person, with a view of warding off disease."

On long exposure to light it disintegrates into a yellow powder known as pararealgar. It was once thought that this powder was the yellow orpiment, but has been recently shown to be the yellow-orange pararealgar.

Realgar, orpiment, and arsenopyrite provide nearly all the world's supply of arsenic as a byproduct of smelting concentrates derived from these ores.

Realgar is also used by firework manufacturers to create the color white in fireworks, manufacturing shot, printing and dyeing calico, and depilating and tanning hides.