Outstanding colorless platy crystals of the very rare borate mineral chelkarite from the type and only known locality worldwide (Chelkar Salt Dome, Aksai Valley, Shalkar, Aktobe Province, Kazakhstan), and associated to hilgardite and anhydrite. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Chelkarite
Chelkarite is an IMA-recognized mineral species in the borate class, with the chemical formula CaMgB₂O₄Cl₂·7H₂O.
It crystallizes in the orthorhombic crystal system (space group Pbca).
Key properties: specific gravity 2.21; optically biaxial.
IMA symbol Cka, IMA status: approved, named in 1968.
Very rare, in the insoluble residue of brines from a salt dome.
It is found associated with Anhydrite, hilgardite, boracite, halite, carnallite, bischofite.
The name is derived from the locality where the first samples were collected, the Chelkar salt dome, Kazakhstan.