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
Category Nesosilicates
Formula
(repeating unit)
Mg3(SiO4)(F,OH)2
IMA symbol Nrb [1]
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
Identification
Formula mass 202.00 g/mol
ColorTan, yellow, yellow-orange, orange-brown, pink with purplish tint, white
Crystal habit Granular, tabular crystals rare
Fracture Uneven to subconchoidal
Tenacity Brittle
Mohs scale hardness6–6.5
Luster Vitreous to resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.177
Optical propertiesBiaxial (+)
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 characteristicsMay fluoresce canary-yellow under SW UV
References [2] [3] [4]

Norbergite is a nesosilicate mineral with formula Mg 3(Si O 4)(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]

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5
(SiO
4
)
2
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2
. Although it is a fairly rare mineral, it is the most frequently encountered member of the humite group of minerals. It is formed in hydrothermal deposits from locally metamorphosed dolomite. It is also found associated with skarn and serpentinite. It was discovered in 1817 at Pargas in Finland, and named from the Greek for "granule", which is a common habit for this mineral.

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References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 Norbergite data on Webmineral
  3. 1 2 Norbergite on Mindat.org
  4. 1 2 Norbergite in the Handbook of Mineralogy
  5. "Norbergite". merriam-webster.com. Merriam-Webster . Retrieved 15 September 2013.