The copper in Michigan's Upper Peninsula mines was deposited from solution over a period of millions of years; when conditions were right it would grow in filaments and sometimes form well-defined crystals. One large and several small whiskers are seen here in a partially-dissolved Calcite matrix; one whisker terminates in a small (ca. 1 mm) crystal of Copper.

Found in the tailings pile of the Caledonia copper mine near Greenland, Michigan, during the Copper Country Mineral Retreat, August 2006.