The White Cap mine is a zoned pegmatite in the Keystone district. A boulder there produced several secondary phosphates of which this is one of them. Ernstite had never been found in the Black Hills prior to this. It was verified by Andy Roberts, The amber brown spray on this specimen is about 1mm and there are a few smaller. These crystals show good terminations, are translucent, and look much like Eosphorite, however they are not bladed but rather prismatic.