Copper 'Skull', Calumet & Hecla Conglomerate, Lake Superior Copper District, Houghton County, Michigan Medium cabinet 6.5 x 10.5 x 13 cm $500. Online 4/8
Copper 'skulls' form as casts or replacements of rhyolite/felsite pebbles in conglomerate. This specimen is a combination of a cast and partial replacement of a cobble. The outside of the cast shows copper 'fins' over the surface that are replacements of smaller attached pebbles. A classic specimen from the district. Mined c. early 1900s. No faults. David Strong Collection.