Atomic Positional Parameters

As1 4e 0.1220 0.0206 0.7639
As2 4e 0.4237 0.8609 0.8558
As3 4e 0.3205 0.8733 0.1772
As4 4e 0.0401 0.8392 0.7149
S1  4e 0.3452 0.0060 0.7014
S2  4e 0.2139 0.0230 0.1157
S3  4e 0.2388 0.7741 0.6392
S4  4e 0.1070 0.7898 0.0511

Reference
Mullen DJE and Nowacki W (1972) Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie, 136, 48

Mineral Chemistry
The mineral realgar, arsenic(II) sulfide, is formed from discrete As₄S₄ molecules. Each arsenic atom binds to one arsenic and three sulphurs, while each sulphur bonds to two arsenics. Realgar is associated with orpiment, other arsenic minerals, and with stibnite (Sb₂S₃) in veins of gold, silver and lead ores. The molecular nature of this mineral may account for it being found as a sublimation product from volcanoes, and as a deposit from hot springs. Realgar is red to red-orange and when exposed to sunlight develops a surface coating of a yellow material now known to be pararealgar, a light-induced polymorph of realgar (Bonazzi et al., 1995; Douglass et al., 1992)

Bonazzi P, Menchetti S and Pratesi G (1995) The crystal structure of pararealgar, As₄S₄. American Mineralogist, 80, 400

Douglass DL, Shing CC and Wang G (1992) The light-induced alteration of realgar to pararealgar. American Mineralogist, 77, 1266


The CHIME figure shows arsenics coloured crimson, sulphurs yellow. The unit cell is outlined.