Atomic Positional Parameters
As1 4e 0.2670 0.1900 0.1430
As2 4e 0.4840 0.3230 0.6430
S1  4e 0.3950 0.1200 0.5000
S2  4e 0.3550 0.3970 0.0130
S3  4e 0.1250 0.2930 0.4100

Reference
Morimoto N (1954) Mineralogical Journal (Japan), 1, 160

Mineral Chemistry
In orpiment, which may contain up to 2.7% antimony, trigonal pyramids of AsS₃ are linked through sulphurs to form corrugated layers perpendicular to the b-axis of the crystal. The lemon-yellow colour of orpiment gives the appearance of gold, hence the Latin name 'auripigmentum' for this mineral. Orpiment, a rare mineral, is associated with realgar, other arsenic minerals, and with stibnite (Sb₂S₃) in veins of gold, silver and lead ores.

The CHIME figure shows arsenic as purple, sulphur yellow. The unit cell is outlined.