Space-filling model of the pararealgar molecule, a mineral form of arsenic sulfde . Colour code: Sulfur, S: yellow Arsenic, As: lilac — Photo: Jynto ( talk ) · CC0
Pararealgar
The arsenic sulfide produced when realgar is exposed to light — the orange-yellow 'pararealgar' on old specimens.
Intro adapted from Wikipedia (CC BY-SA).
Pararealgar is an IMA-recognized mineral species in the sulfide class, with the chemical formula As₄S₄.
It crystallizes in the monoclinic crystal system (space group P2_1/n).
Key properties: Mohs hardness 1–1.5; specific gravity 3.52; Bright yellow streak; Vitreous to resinous luster.
IMA symbol Prlg, IMA status: approved, named in 1980.
An alteration product of realgar in stibnite-bearing quartz veins, the alteration typically a result of exposure to light.
It is found associated with Realgar, stibnite, tetrahedrite, arsenopyrite, duranusite, arsenic, arsenolite, sulfur, lepidocrocite, pyrite.
In allusion to its chemical identity with realgar.