Norbergite

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Norbergite
Norbergite-Calcite-290476.jpg
Norbergite crystals on calcite from Oakssaung Hill, Mogok, Mandalay, Burma (size: 4.2 x 3.3 x 2.3 cm)
General
CategoryNesosilicates
Formula
(repeating unit)
Mg3(SiO4)(F,OH)2
IMA symbolNrb[1]
Strunz classification9.AF.40
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnma
Unit cella = 8.747(6), b = 4.710(4)
c = 10.271(8) [Å]; Z = 4
Identification
Formula mass202.00 g/mol
ColorTan, yellow, yellow-orange, orange-brown, pink with purplish tint, white
Crystal habitGranular, tabular crystals rare
FractureUneven to subconchoidal
TenacityBrittle
Mohs scale hardness6-6.5
LusterVitreous to resinous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.177
Optical propertiesBiaxial (+)
Refractive indexnα = 1.563 nβ = 1.567 nγ = 1.590
Birefringenceδ = 0.027
PleochroismPleochroism: X = pale yellow; Y = very pale yellow; Z = colorless
2V angle44 - 50°
Other characteristicsMay fluoresce canary-yellow under SW UV
References[2][3][4]

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.[2][3][5] 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.[4]

References[edit]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85: 291–320.
  2. ^ a b Norbergite data on Webmineral
  3. ^ a b Norbergite on Mindat.org
  4. ^ a b Norbergite in the Handbook of Mineralogy
  5. ^ "Norbergite". merriam-webster.com. Merriam-Webster. Retrieved 15 September 2013.