Pararealgar

Pararealgar is an arsenic with the chemical formula As4S4 also represented as AsS. It forms gradually from realgar under exposure to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4. It is soft with a Mohs hardness of 1 - 1.5, is yellow orange in colour, and its monoclinic crystals are very brittle, easily crumbling to powder.

It is one of the sulfides of arsenic and is one of two isomers of As4S4. It forms upon exposure of the symmetrical isomer to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4.