Description: Presley Wash obsidian is actually a sub-vitreous rhyolite ranging from black to gray-green to opaque gray. Sanidine phenocrysts are often present in the matrix, as seen in both samples depicted here. The source of this material is in Presley Wash, east of Round Mountain, Arizona, and in the alluvium south of the juncture of Partridge Creek and Presley Wash in the same area.