This is a fascinating and unique pseudomorph from the Phoenix Mine. The copper grew over a cluster of parallel wedge-shaped crystals of an unknown mineral, perhaps anhydrite, to form this intriguing cast. The shape of the casts is reminiscent of the “lady’s slipper” pseudomorphs from the Virtuous Lady Mine in Devon, England. These are always referred to as being pseudomorphs after barite, but perhaps they need more research as well.