Callaghanite Field of view: 0.5 mm Locality: Lichtloch 26, Hettstedt, Mansfeld-Südharz, Saxony-Anhalt, Germany — Photo: Henk Smeets – tomeikminerals.com · CC BY 4.0
Callaghanite
Callaghanite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Cu₂Mg₂(CO₃)(OH)₆·2H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 3–3.5; specific gravity 2.71; White streak; Vitreous luster; optically biaxial.
IMA symbol Cgh, grandfathered status — known before the IMA’s founding, named in 1954.
Disseminated in the contact zone between diorite and serpentinized dolostone.
It is found associated with Magnesite, dolomite, serpentine, brucite, forsterite.
The mineral was named to honor Dr. Eugene Callaghan (1904–1990), Director of the New Mexico Bureau of Mines, Socorro, New Mexico, USA, for his work on magnesite deposits.