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Norbergite crystals on calcite from Oakssaung Hill, Mogok, Mandalay, Burma (size: 4.2 x 3.3 x 2.3 cm)
Category Nesosilicates
(repeating unit)
Strunz classification 9.AF.40
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnma
Unit cell a = 8.747(6), b = 4.710(4)
c = 10.271(8) [Å]; Z = 4
Formula mass 202.00 g/mol
Color Tan, yellow, yellow-orange, orange-brown, pink with purplish tint, white
Crystal habit Granular, tabular crystals rare
Fracture Uneven to subconchoidal
Tenacity Brittle
Mohs scale hardness 6-6.5
Luster Vitreous to resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.177
Optical properties Biaxial (+)
Refractive index nα = 1.563 nβ = 1.567 nγ = 1.590
Birefringence δ = 0.027
Pleochroism Pleochroism: X = pale yellow; Y = very pale yellow; Z = colorless
2V angle 44 - 50°
Other characteristics May fluoresce canary-yellow under SW UV
References [1][2][3]

Norbergite is a nesosilicate mineral with formula Mg3(SiO4)(F,OH)2. It is a member of the humite group.

It was first described in 1926 for an occurrence in the Östanmoss iron mine in Norberg, Västmanland, Sweden, for which it is named.[1][2][4] It occurs in contact metamorphic zones in carbonate rocks intruded by plutonic rocks or pegmatites supplying the fluorine. Associated minerals include dolomite, calcite, tremolite, grossular, wollastonite, forsterite, monticellite, cuspidine, fluoborite, ludwigite, fluorite and phlogopite.[3]