Isokite
Isokite is an IMA-recognized mineral species in the phosphate class, with the chemical formula CaMg(PO₄)F.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Titanite structural group.
Key properties: Mohs hardness 4.5–5; specific gravity 3.15–3.27; Silky (fibers), slightly pearly (plates) luster; optically biaxial.
IMA symbol Iso, grandfathered status — known before the IMA’s founding, named in 1955.
A late-stage metasomatic mineral in ankeritic carbonatite (Nkombwa Hill); replacing wagnerite in a pegmatite dike in sillimanite grade gneiss (Benson mines); an alteration product of triplite in granite pegmatite (Mangualde and Ribeira.
It is found associated with Dolomite, strontian fluorapatite, monazite, daqingshanite-(Ce), strontianite, quartz, phlogopite, pyrochlore (Nkombwa Hill, Zambia).
The name refers to Isoka, Zambia, the town near which the first specimens were collected.