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Atomic Positional Parameters
As 6c 0.0000 0.0000 0.2271

Reference
Schiferl D and Barrett CS (1969)
Journal of Applied Crystallography, 2, 30

Mineral Chemistry
Elemental arsenic is a rare mineral found in hydrothermal veins associated with ores of silver, cobalt and nickel. Antimony (Sb) and bismuth (Bi) share the same crystal structure. Although the structure is based on cubic close-packing, sheets of arsenic atoms separate into pairs with arsenic-arsenic bond distances within sheets being shorter than bonds between closest atoms between sheets. Each arsenic atom is joined to its nearest three neighbours in pyramidal coordination.

The most abundant arsenic bearing mineral is arsenopyrite, also known as mispickel, which has the formula FeAsS. Other arsenic bearing minerals include niccolite (NiAs), enargite (Cu₃AsS₄), sperrylite (PtAs₂), cobaltite (CoAsS), loellingite (FeAs₂), realgar (AsS) and orpiment (As₂S₃).

The CHIME figure shows arsenic atoms as crimson spheres. The unit cell is outlined. Note the pyramidal coordination of each arsenic atom.