Two distinct modifications of AsS occur in the Alacran Ag-As-Sb vein deposit in northern Chile. Of these, one, which crystallized early in the development of the deposit, apparently corresponds to the high temperature alpha-AsS polymorph, not previously documented from natural assemblages. Realgar which occurs as euhedral crystals in median vein cavities is similar, but not identical to normal realgar, or beta-AsS, from other localities. The relationships between the two forms are poorly-defined, but neither exhibits instability on exposure to light or to infrared radiation.