Calumetite is a rare mineral belonging to the halide group, specifically the chloride class. It is a distinctive mineral known for its unique crystal structure and composition. The name "calumetite" is derived from the French word "calumet," meaning a ceremonial pipe or peace pipe, owing to its historical association with Native American cultures.
Chemically, calumetite is composed of copper, chlorine, and oxygen, with the chemical formula Cu_5Cl_2(OH)_8·2H_2O. It typically forms as tabular, bladed crystals that can occur as single individuals or in aggregates. The crystals have a bright green color and are translucent to transparent, often exhibiting vitreous to pearly luster.
Calumetite is primarily found within copper mineralization deposits, commonly associated with other secondary copper minerals. It is typically formed through the oxidation of primary copper sulfides, specifically chalcocite and covellite, in the presence of chloride-rich solutions. Calumetite is found in a limited number of global localities, including the famous Keweenaw Peninsula in Michigan, USA, where it was first discovered.
Due to its rarity and distinctive crystal habit, calumetite is highly sought after by mineral collectors. Its cultural significance also adds to its desirability. While it may lack any significant industrial uses, calumetite holds great value in the world of mineralogy due to its aesthetic appeal, historical connections, and geological significance.
