Jahnsite-(CaMnMg)
Jahnsite-(CaMnMg) is an IMA-recognized mineral species in the phosphate class, with the chemical formula CaMn²⁺Mg₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O.
It crystallizes in the monoclinic crystal system (space group P2/a). It is a member of the Jahnsite structural group.
Key properties: Mohs hardness 4; specific gravity 2.71–2.72; Vitreous to subadamantine luster; optically biaxial.
IMA symbol Jah-CaMnMg, IMA status: approved, named in 1973.
A late-stage hydrothermal decomposition product of primary triphylite- lithiophilite in complex granite pegmatites.
It is found associated with Leucophosphite, huréaulite, collinsite, ferrisicklerite, robertsite, rockbridgeite, triphylite, tavorite, messelite, vivianite (Custer Co., South Dakota, USA).
The mineral was named to honor Professor Richard Henry Jahns (1915–1983), specialist in pegmatite mineralogy, Stanford University, California, USA.