This is a world-class competition-quality thumbnail of the rare silver & selenium sulfide, aguilarite. The superb specimen consists of chevron-like crystals which clearly exhibit hopper growth where the crystal edges grew faster than the centers (common in so many Mexican silver species). The color is a dark gray color with a matte finish. The specimen was photographed and illustrated in the Mineralogical Record, May-June 1999, Vol. 30 page 212, fig. 4 in an important article on the locality, and is one of the few verifiable examples of this mineral species that I have ever seen on the market. It is razor sharp! From the noted thumbnail collection of Ron Pellar, by exchange to me long ago.