It is orange-red in color, melts at 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur.

[2] Its name comes from the Arabic rahj al-ġār (رهج الغار [rahdʒælɣaːr] listenⓘ, "powder of the mine"), via Medieval Latin, and its earliest record in English is in the 1390s.

It was sometimes used to kill weeds, insects, and rodents,[11] even though more effective arsenic-based anti-pest agents are available such as cacodylic acid, (CH3)2As(O)OH, an organoarsenic compound used as herbicide.

[12] The Greek physician Nicander described a death by "bull's blood", which matches the known effects of arsenic poisoning.

Early occurrences of realgar as a red paint pigment are known for works of art from China, India, Central Asia, and Egypt.

In the US it occurs notably in Mercur, Utah; Manhattan, Nevada; and in the geyser deposits of Yellowstone National Park.