What is Nuummite?
Nuummite is a dark iridescent lapidary variety of anthophyllite-gedrite amphibole, prized for flashes of gold and bronze from its fibrous intergrowths.
Mineralogy and crystal structure
Reference formula: Mg7Si8O22(OH)2. Nuummite is a variety or lapidary material rather than a separate fixed mineral species. Its optical flash comes from amphibole intergrowths and orientation; the displayed model is a representative anthophyllite structure, not a universal composition. Nuummite is classified with silicates and has a orthorhombic crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 2.9–3.2.
Colour, lustre and habit
Typical colours include black, brown, golden, bronze. The usual fibrous, massive, foliated habit and vitreous, silky, sub-metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Nuummite forms in or is associated with high-grade metamorphism of magnesium-rich ultramafic rocks and amphibolite-facies assemblages. Important documented localities include Greenland, especially the Nuuk region, with related amphibole materials reported elsewhere.
Gold flashes inside a dark metamorphic stone
Nuummite is popular because it looks almost metallic while remaining unmistakably natural. Rotating a polished piece reveals flashes generated by amphibole intergrowth, turning structure and orientation into a dramatic visual effect.
Collecting and care
Protect polished surfaces from scratches and acids; disclose locality and variety status for commercial material.
