When it comes to Michigan copper, I am quite picky.  There is a nearly endless supply of twisted chunks and bits-- occasionally you will get a crude crystal that must be half-way imagined, or a crystal random face. But I like the sharp ones-- the specimens that leave no doubt that what you are looking at is in fact a copper crystal. This one fits the requirement, with a cluster of elongated crystals rising out of a matrix of more copper crystals. The chocolaty patina is particularly good one this one.