Red single crystal of the rare borate mineral congolite from Germany (Bischofferode Potash Works, Bleicherode, Nordhausen, Thuringia, Germany). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Congolite
Congolite is an IMA-recognized mineral species in the halide class, with the chemical formula Fe²⁺₃B₇O₁₃Cl.
It crystallizes in the hexagonal crystal system (space group R3c). It is a member of the Boracite structural group.
Key properties: Mohs hardness 7; specific gravity 3.58; optically uniaxial.
IMA symbol Cgl, IMA status: approved, named in 1971.
Part of insoluble residue from a drill core into sedimentary evaporites (Brazzaville, Congo); in a marine evaporite deposit (Penobsquis mine, Canada).
It is found associated with Anhydrite, halite (Brazzaville, Congo).
The name refers to Congo, the country in which the first specimens were collected.