Nuummite

Nuummite
General
CategoryMineral variety
Formula(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
Density2.85 - 3.57
Refractive index1.598 - 1.697 Biaxial
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 magnification

Nuummite, usually black in colour and opaque, 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 formed due to two consecutive metamorphic overprints of an originally igneous rock. The intrusion took place in the Archean around 2800 million years ago, the metamorphic overprints have been dated at 2700 and 2500 million years ago.[citation needed]

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. 1 2 "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