Norbergite , Calcite Locality: Oakssaung Hill, Mogok , Sagaing District, Mandalay Division , Burma (Myanmar) ( Locality at mindat.org ) Size: 4.2 x 3.3 x 2.3 cm. Norbergite is a rare magnesium silicate. Three gemmy and lustrous, orange-yellow norbergite crystals to 1.5 cm are frozen in a cleavage fragment of gray calcite on this rare specimen from Mogok, Burma. Very seldom available in crystals this size and gemminess. Found in 2003-2004. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Norbergite
A magnesium silicate-fluoride of the humite group, described in 1926 from Sweden's Norberg iron mine.
Intro adapted from Wikipedia (CC BY-SA).
Norbergite is an IMA-recognized mineral species in the silicate class, with the chemical formula Mg₃(SiO₄)F₂.
It crystallizes in the orthorhombic crystal system (space group Pbnm). It is a member of the Humite structural group.
Key properties: Mohs hardness 6–6.5; specific gravity 3.177; Vitreous to resinous luster; refractive index 1.573; optically biaxial.
IMA symbol Nrb, grandfathered status — known before the IMA’s founding, named in 1926.
Found in contact metamorphic zones in limestones and dolostones into which plutonic rocks or pegmatites have introduced fluorine.
It is found associated with Dolomite, calcite, tremolite, grossular, wollastonite, forsterite, monticellite, cuspidine, fluoborite, ludwigite, fluorite, phlogopite. Ä.
The name comes from its first locality at Norberg, Sweden.