Nuummite – what kind of stone is it?
Nuummite (also written nuumit or nuummite) is not a single mineral, but a metamorphic rock consisting of intergrown amphibole minerals – typically anthophyllite and gedrite. The elongated crystals lie almost parallel, and it is these that give the stone its characteristic golden, blue-green, and copper-coloured flashes against a black background. The name comes from Nuuk, where the material originates.
How the play of colour works
Geology, not healing: We describe mineralogy, origin, and appearance – not effects or healing claims.
Fact-based reference knowledge: Origin, mineralogy, colour, and hardness in one place – written for jewellery makers and collectors.
Our own stones in stock: However, we have thousands of genuine stones and crystals in our shop at Nybrovej 83 in Gentofte.
Why does Nuummite shimmer?
The play of colour is not due to pigment, but light reflecting and refracting within densely packed, elongated amphibole crystals. Because the crystals are aligned in specific directions, the flash is only visible from certain angles – this makes a Nuummite cabochon appear 'alive' when rotated.
This also means that the cutting direction is crucial. An incorrectly oriented cut can result in an almost entirely black stone with no play of colour, even if the material itself is good.
Nuummit, nuummite, or nummit?
All three spellings are used interchangeably in trade for the same material. As Nuummite is a rock and not an approved mineral name, there is no single official mineralogical designation, and the name is also applied to similar amphibole rocks from other localities. If the origin is important to you, it should be specifically stated in the product description.
Quality and Processing
- Good material exhibits play of colour across the entire polished surface – not just in a single band.
- The width of the shimmering streaks varies; both fine and coarse patterns exist.
- The polish must be high, otherwise the play of colour will be noticeably dulled.
- Fissures and inclusions occur and should be disclosed by the seller.
How to use this page
This page is designed as a knowledge resource for jewellery makers and collectors: covering the stone's geological nature, origin, appearance, and considerations for processing and authenticity.
If you wish to work further with natural stones, you can find overviews of genuine stones, crystals, and semi-precious stones – strings, loose beads, and rough chunks – under Stones & Crystals.
FAQ
Is nuummite a mineral?
No, it's a rock. It mainly consists of the intergrown amphibole minerals anthophyllite and gedrite, and their orientation gives it its iridescence.
How old is nuummite?
Material from the Nuuk area dates back to the Archaean Eon and is among the oldest known rocks on Earth – in the order of three billion years.
Is nuummite water resistant?
Yes, polished nuummite can withstand a brief rinse in lukewarm water. Avoid ultrasonic cleaning, soap, and chemicals, which can damage fissures and fillings.