Nuummite
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| Nuummite | |
|---|---|
 | |
| General | |
| Category | Mineral variety |
| Formula | (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]
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.[citation needed]
