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Calumetite; Jeff Weissman / Photographic Guide to Mineral Species at Web Mineral: Link


A light blue copper corrosion product that rarely occurs as a mineral. As a mineral, it was discovered in 1963 at the Centennial Miner near Calumet, Michigan. Calumetite has been identified as a copper corrosion product on bronzes (Scott 2000).

Physical and Chemical Properties

  • Composition = Cu(OH, Cl)2 - 2(H2O)
  • Description = azure to light blue crystals (orthorhombic)
  • Streak = bluish-white
  • Luster = pearly
  • Hardness = 2

Resources and Citations

  • David Scott, 'A Review of Copper Chlorides and Related Salts in Bronze Corrosion and as Painting Pigments'. Studies in Conservation, 45, 39-54, (2000).