A really, really good copper specimen-- to begin with the crystal is exceptionally sharp, then it is very well isolated-- in fact I think just calling it "isolated" doesn't stress the point enough-- it is surrounded by contrasting white datolite, *and* the exact locality information was preserved-- non of these things are normal when it comes to Michigan copper.  Usually, if a specimen has crystals, they will be semi-rounded, then they are almost always often clustered together, and often without precise locality information.