Copper: Fissure Vein Deposits, Keweenaw County, Michigan USA

This is a superb large thumbnail (“toenail”) sized group of sharp cubic copper crystals without matrix. Well-formed cubes are arguably the rarest crystal form in Michigan copper, and this is a fantastic thumbnail consisting of a very 3-dimensional group of cubes in parallel-growth. The copper cubes are up to ~7 mm and have great patina. A rare Michigan Copper Country classic. Annette Slade photo.