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Nuummite

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Rare metamorphic rock
Nuummite
General
CategoryMineral variety
Formula
(repeating unit)		(Mg
2)(Mg
5)Si
8O
22(OH)
2
Identification
Formula mass780.82 gm
ColorBlack, grey
TwinningNone
CleavagePerfect on 210
FractureConchoidal
Mohs scale hardness5.5 - 6.0
LusterVitreous/glossy
Diaphaneityopaque
Specific gravity3.18–3.37
Density2.85 - 3.57
Optical propertiesBiaxial (–)
Refractive index1.598 - 1.697
Birefringence0.0170 - 0.230

Nuummite is a rare metamorphic rock that consists of the amphibole minerals gedrite and anthophyllite. It is named after the area of Nuuk in Greenland, where it was found.

Description

Nuummite under 240x magnifiication

Nuummite is usually black in colour and opaque. It consists of two amphiboles, gedrite and anthophyllite, which form exsolution lamellae that give the rock its typical iridescence. Other common minerals in the rock are pyrite, pyrrhotite and chalcopyrite, which form shimmering yellow bands in polished specimens.

In Greenland the rock was formed by two consecutive metamorphic overprints of an originally igneous rock. The intrusion took place in the Archean around 2800 million years ago and the metamorphic overprint was dated at 2700 and 2500 million years ago.

History

The rock was first discovered in 1810 in Greenland by the mineralogist K. L. Giesecke. It was defined scientifically by O. B. Bøggild between 1905 and 1924.

In 2009, a new variety of Nuummite was discovered in central Mauritania. Under its unofficial name Jenakite, this variety is distinctive due to the presence and high density of blue and green anthophyllite needle-like crystals. It has no golden anthophyllite needle-like crystals.

Nuummite from Greenland predominantly has golden and occasionally blue anthophyllite needle-like crystals.

References

  1. Geological Survey of Denmark and Greenland (GEUS), ed. (2008), "Minerals in Greenland" (PDF), Geology and Ore (in German), no. 12, p. 12, archived from the original (PDF) on 2011-12-21, retrieved 2012-11-08
  2. "Nuumite". ClassicGems.net. Retrieved 1 December 2012.
  3. ^ "Gemstones of Greenland" (PDF). Geology and Ore. Geological Survey of Denmark and Greenland (GEUS). January 2007. Archived from the original (PDF) on 24 February 2013. Retrieved 4 December 2012.
  4. K. Secher & P. Appel (January 2007). "Gemstones of Greenland - Exploration and Mining in Greenland". Geology and Ore. 7: 9. Archived from the original on 21 December 2011. Retrieved 8 November 2012.
  5. P. E. Champness, K. A. Rodgers (October 2000). "The origin of iridescence in anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland.". Mineralogical Magazine. 64 (5.1): 885–889. Bibcode:2000MinM...64..885C. doi:10.1180/002646100549715. S2CID 140574142.

Further reading

  • P. W. U. Appel & A. Jensen: A new gem material from Greenland: iridescent orthoamphibole . Gems and Gemology, 23, P. 3642, 1987 (Online Extract)
  • K. A. Rodgers et al.: Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland. Composition, exsolution, age. Mineralogical Magazine, Vol. 60, P. 937–947, December 1996 (Online Extract)


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