metamorphic
Nuummite
Nuummite (Orthoamphibole rock composed of Anthophyllite and Gedrite, (Mg,Fe)7Si8O22(OH)2)
Hardness: 5.5-6.0; Color: Charcoal gray to black with iridescent flashes of gold, copper, blue, or red; Luster: Vitreous to sub-metallic; Crystal structure: Orthorhombic; Cleavage: Perfect in two directions; Specific Gravity: 3.2-3.5
- Hardness
- 5
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 5.5-6.0; Color: Charcoal gray to black with iridescent flashes of gold, copper, blue, or red; Luster: Vitreous to sub-metallic; Crystal structure: Orthorhombic; Cleavage: Perfect in two directions; Specific Gravity: 3.2-3.5
Formation & geological history
Formed through high-grade regional metamorphism of igneous precursors. It is one of the oldest rocks on Earth, dating back approximately 3 billion years to the Archean Eon. Found primarily in metamorphic belts of Greenland.
Uses & applications
Primarily used for high-end jewelry, lapidary art, and as a collector's specimen. It is valued for its unique 'schiller' effect (iridescence) produced by the lamellar structure of the minerals.
Geological facts
Known as the oldest rock on Earth, it was discovered in 1982 near Nuuk, Greenland, from which it takes its name. The iridescence is caused by light scattering between alternating microscopic layers of the minerals anthophyllite and gedrite.
Field identification & locations
Identify in the field by searching for the chatoyant 'flecking' against a dark, splintery-textured groundmass. Found almost exclusively in the Nuuk region of Greenland, though similar material has been found in Canada and the US. Collectors should look for vibrant flashes covering the specimen.
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