Geographic Minerals



Calumetite is a natural rarely occurring mineral. It was discovered in 1963 at the Centennial Mine near Calumet, Michigan, United States. It was named after the town of Calumet in Michigan, USA, where it was first discovered. It was first discovered along with anthonyite. It has a chemical formula of Cu(OH, Cl)2•2(H2O). It is a rare mineral with additional localities in Greece, Germany, Italy, and Austria.

General Information

  • Category: Halide minerals
  • Formula: Cu(OH, Cl)22(H2O)
  • Crystal system: Orthorhombic
  • Color: Azure blue; Powder blue
  • Luster: Pearly.


Calumetite can be identified in the field by its color variations, such as azure-blue, powder blue, and bluish-white. Its opaque form has {001} perfect cleavage. This mineral has a pearly luster, with a blue streak. The fracture of this mineral is brittle.

The density of calumetite is 7.2 to 7.4 g/cm3, with a hardness of 2 – approximate to gypsum.

  • Mohs scale hardness: 2
  • Lustre: Pearly
  • Comment: On basal cleavages
  • Colour: Azure blue; Powder blue
  • Comment: In masses: Brilliant azure blue inclining to powder blue
  • Tenacity: Brittle

Calumetite has a bluish-white streak. Its luster is pearly on cleavage. It has a brittle tenacity and is semitransparent. The specific gravity of calumetite could not be measured because of the difficulty in separating the quartz and epidote from the calumetite mineral coating them.

Geologic occurrence

Calumetite occurs in cavities and fractures in basalt, formed by the action of chlorine-bearing connate waters on copper, with cuprite being regarded as an intermediate product in the alteration. It is often associated with minerals such as tremolite, monazite, quartz, epidote, copper, cuprite, paratacamite, atacamite, buttgenbachite, malachite, and anthonyite.

Calumetite has been found in basalt cavities. It was prepared with ammonium chloride by means of the lime blue recipe which showed that the mineral is synthetic. It was first discovered in Calumet Michigan but has since been observed in other mines near the Calumet mine.


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