Calciomurmanite
Calciomurmanite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na, )₂Ca(Ti,Mg,Nb)₄[Si₂O₇]₂O₂(OH,O)₂(H₂O)₄.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Seidozerite-Murmanite structural group.
Key properties: Mohs hardness 2.5–3; specific gravity 2.7; White streak; Pearly on cleavage; greasy on fracture surfaces luster; optically biaxial.
IMA symbol Cmmn, IMA status: approved, named in 2015.
Formed by late-stage, low-temperature hydrothermal alteration (hydration and natural cation exchange) of a high-temperature, anhydrous phosphate-bearing titanosilicate, most likely lomonosovite and/or betalomonosovite.
It is found associated with Microcline, aegirine, lorenzenite, fluorapatite (Mt Flora); microcline, aegirine, lamprophyllite, tsepinite-Ca, tsepinite-K (Mt. Eveslogchorr).
As an analogue of murmanite with essential calcium and sodium.