Gem library
Nuummite
Three billion years of dark fire
Nuummite is one of the oldest ornamental rocks anyone can hold: about three billion years. Its black ground lights up with golden, blue and green flashes that move with the light, and that fire comes from the very structure of the rock.
- Hardness (Mohs)
- 5.5 – 6
- Density
- 2.85 – 3.57
- Crystal system
- Orthorhombic
- Refractive index
- 1.598 – 1.674
- Cleavage
- Perfect in the constituent crystals
Mineralogical identity
- Family
- Metamorphic rock (amphibolite)
- Species
- Anthophyllite and gedrite
- Variety
- Greenland nuummite
- Chemical formula
- (Mg,Fe)₇Si₈O₂₂(OH)₂
- Crystal system
- Orthorhombic (aggregate of lamellae)
- Classification
- Ornamental rock
- Rarity
- Rare
- Indicative price
- €2 – 40/ct
Etymology
From Nuuk, the capital of Greenland, near which the rock was identified in 1810. The suffix -mite follows the Greenlandic habit of naming places.
Physical & optical properties
- Hardness (Mohs)
- 5.5 – 6
- Density
- 2.85 – 3.57
- Refractive index
- 1.598 – 1.674
- Birefringence
- 0.015 – 0.025
- Cleavage
- Perfect in the constituent crystals
- Fracture
- Uneven
- Lustre
- Silky to submetallic
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- black, anthracite grey, iridescent, golden, blue
Formation, geology & history
Three billion years, and an unmixing
The original rock was an Archaean magmatic intrusion, emplaced about 2.8 billion years ago in what is now south-west Greenland. Two metamorphic episodes, around 2.7 and then 2.5 billion years ago, turned it into amphibolite. During that very slow cooling, an initially homogeneous mineral unmixed into two distinct amphiboles, anthophyllite and gedrite, which organised themselves into alternating lamellae of micrometre thickness. It is that layering at the scale of the wavelength of light that produces the iridescence: the same mechanism as the adularescence of moonstone, or the colours of a soap bubble.
A fire that is not a colour
The golden, coppery, blue and green flashes of nuummite are not pigments: they are interference. Depending on the local thickness of the lamellae, the reflected light is shifted towards one colour or another, and the fire moves as the stone moves. A well-oriented piece shows whole bands lighting up and going out. The lapidary has to find the plane that maximises the effect, and that takes time: on a block, the favourable orientation cannot be guessed from the outside, and a cut across the grain gives a black, dull stone. The yield is low, which explains the price.
A difficult extraction
The deposit on the Nuuk peninsula is reached by boat, in an area where the working season is short. Extraction is regulated by the Greenlandic government and production remains artisanal, of the order of a few tonnes a year. The Mauritanian material found in 2009, sometimes called jenakite, is a neighbouring rock with comparable flashes but of another geological origin; it arrives in greater quantity and costs less. Many stones sold as nuummite come from there, which is not illegitimate if it is stated.
How to recognise it
- The fire movesTilt the stone under a point source: the golden and blue patches should light up and go out in succession. A fixed speckled black is not nuummite.
- The lamellar structureUnder a loupe, the iridescence follows elongated parallel bands, not scattered points. That is the trace of the amphiboles unmixing.
- Hardness 5.5 to 6It scratches glass with difficulty and yields to a good file. Softer than quartz, harder than an obsidian scratched by steel.
Imitations, treatments & confusions
- Black aventurine glassGlass loaded with copper flakes, sold as cabochons. The flakes there are identical, scattered at random, and the effect does not travel in bands.
- Dark labradorite sold as nuummiteSpectrolite labradorite is strongly iridescent but it is a feldspar, lighter (2.7) and with visible flat cleavages.
- Undeclared Mauritanian materialAuthentic and close, but it is not Greenland nuummite and it is worth distinctly less. Ask for the origin.
Deposits & origins
Greenland (the Nuuk region, the original deposit), Mauritania (found in 2009, a neighbouring material), Spain, Russia, United States
Care & precautions
- Warm soapy water and a soft cloth. Dry at once.
- No ultrasonics: the lamellar planes are so many surfaces of weakness.
- Does not mind light, the effect is structural and does not fade.
- Store separately, the polish scratches and the fire goes out on a dulled surface.
Traditions & crystal healing
- Chakras
- Root · third eye
- Zodiac signs
- Scorpio · Capricorn
- Element
- Earth
The Inuit saw in it a stone of power reserved for shamans, and modern tradition has made it a stone of deep grounding and inner work. In the shops it is one of the few stones whose sales pitch mentions its age. Cultural heritage, never medicine.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Why does my nuummite shine on one side only?
Because the lamellae have a single orientation in the rock. The lapidary chooses the most favourable plane, but the effect stays directional: that is normal, and it is in fact proof that it is authentic.
Greenland or Mauritanian nuummite?
Both exist and look alike. The Greenlandic material is the original, rarer and dearer. A very low price points to Mauritania, which is honest if it is declared.
Can it be worn as a ring?
Yes with care. Hardness 6, good toughness, but a scratched polish makes the fire disappear, and the fire is the whole point of the stone.
Tools for this stone
Nuummite: only the tools this stone actually concerns, each carrying the value read on this page.