Nuummite
| Nuummite | |
|---|---|
| General | |
| Category | Mineral variety |
| Formula (repeating unit) |
(Mg 2)(Mg 5)Si 8O 22(OH) 2 |
| Identification | |
| Formula mass | 780.82 gm |
| Color | Black, grey |
| Twinning | None |
| Cleavage | Perfect on 210 |
| Fracture | Conchoidal |
| Mohs scale hardness | 5.5 - 6.0 |
| Luster | Vitreous/glossy |
| Diaphaneity | opaque |
| Density | 2.85 - 3.57 |
| Refractive index | 1.598 - 1.697 Biaxial |
| Birefringence | 0.0170 - 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.[1][2][3]
Description
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.[3] 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.[4] It was defined scientifically by O. B. Bøggild between 1905 and 1924.[5] True Nuummite is only found in Greenland. Due to its iridescent nature, this rare stone is sought after by gemstone dealers, collectors and those interested in the esoteric. It is often sold with tumble finishing.
References
- ↑ Geological Survey of Denmark and Greenland (GEUS), ed. (2008), "Minerals in Greenland" (in German), Geology and Ore (12): pp. 12, http://www.geus.dk/minex/go12.pdf
- ↑ "Nuumite". ClassicGems.net. Retrieved 1 December 2012.
- 1 2 "Gemstones of Greenland" (PDF). Geology and Ore. Geological Survey of Denmark and Greenland (GEUS). January 2007. Retrieved 4 December 2012.
- ↑ K. Secher & P. Appel (January 2007). "Gemstones of Greenland - Exploration and Mining in Greenland.". Geology and Ore. 7: 9. Retrieved 8 November 2012.
- ↑ 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. doi:10.1180/002646100549715. Retrieved 8 November 2012.
Further reading
- P. W. U. Appel & A. Jensen: A new gem material from Greenland: iridescent orthoamphibole [nuummite]. 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)