Grenmarite
Grenmarite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₂Zr₂Na₂MnZr(Si₂O₇)₂O₂F₂.
It crystallizes in the monoclinic crystal system (space group P2/c). It is a member of the Seidozerite-Rinkite structural group.
Key properties: Mohs hardness 4.5; specific gravity 3.49; Pale yellowish-brown streak; Vitreous luster; optically biaxial.
IMA symbol Grn, IMA status: approved, named in 2003.
An early crystallization product, embedded in microcline and fine-grained albite in an alkaline nepheline syenite pegmatite dike cutting larvikite.
It is found associated with Microcline, aegirine, biotite, nepheline, albite, astrophyllite, låvenite, catapleiite, leucophanite, pyrochlore, fluorite, and minor molybdenite, sphalerite.
The name refers to Grenmar, the Norse name of the Langesundsfjord.