These cornetite crystals are from the Star of the Congo Mine (L’toile du Congo Mine) in Lubumbashi, Katanga, Congo.This area is in the Katanga Copper Cresent which contains many copper and copper mineral deposits. Cornetite is a copper sulfate containing the containing the elements Cu, P, O and H. This specimen consists of a sandstone matrix with contrasting blue crystals scattered over the surface. These crystals vary in morphology from, dipyramidal, double terminated to minute crystal clusters. They have a bright vitreous luster. The largest crystals measure approximately 1.5 mm.This piece measures 2 3/4 x 1 3/4 x 3/4 inches or 70 x 45 x 19 mm.