The facts
What eclogite actually is
Mineralogically, eclogite is a high-pressure metamorphic rock of red pyrope-almandine garnet in green omphacite pyroxene, formed in subduction zones — Garnet (Mg,Fe,Ca)3Al2(SiO4)3 and omphacite (Ca,Na)(Mg,Fe,Al)Si2O6, with rutile, kyanite and coesite in the ultra-high-pressure examples, crystallising in the aggregate system.
The colour is caused by fe and Mg in garnet for red, Fe and Na in omphacite for green. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.67-1.79 (mixed), and the specific gravity sits near 3.30-3.60 - unusually heavy, which is diagnostic in the hand; cleavage is pyroxene cleavage; garnet none.
Where eclogite comes from
The recognised sources are Nordfjord and the Western Gneiss Region, Norway, Dora Maira massif, Piedmont, Italy (coesite-bearing UHP eclogite), Dabie Shan and Sulu, China and Kimberlite xenoliths, Roberts Victor mine, South Africa (diamond-bearing eclogite).
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How eclogite is treated
Untreated; polished as a specimen and occasionally as ornamental stone. Scientifically it is one of the most important rock types there is - the coesite and microdiamond discoveries in Dora Maira and Dabie eclogites established continental ultra-high-pressure metamorphism. Diamond-bearing eclogite xenoliths from kimberlite are collector items with real value. Not CITES.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What eclogite is confused with
The usual confusions are Garnet amphibolite, Anyolite (ruby-in-zoisite), Granulite and Dyed composites.
The separation is rarely a matter of opinion: refractive index 1.67-1.79 (mixed) and specific gravity 3.30-3.60 - unusually heavy, which is diagnostic in the hand settle most of it in a minute, and magnification settles the rest.
What eclogite is used for
Eclogite is bought by mineral collecting, decorative objects and architecture and interiors — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the specimen, by the piece or by the square metre.
Durability and care
Eclogite is 6-7.5 on the Mohs scale, with pyroxene cleavage; garnet none cleavage.
With no cleavage plane to worry about, the practical limit is abrasion rather than breakage, and it takes daily wear well.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What eclogite costs
Indicative pricing for eclogite is $10-80 per kilogram for ornamental slabs; diamond-bearing xenoliths from named kimberlites $200-5,000 per specimen.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is eclogite treated, and how?
Untreated; polished as a specimen and occasionally as ornamental stone. Scientifically it is one of the most important rock types there is - the coesite and microdiamond discoveries in Dora Maira and Dabie eclogites established continental ultra-high-pressure metamorphism. Diamond-bearing eclogite xenoliths from kimberlite are collector items with real value. Not CITES.
Where does eclogite come from?
Nordfjord and the Western Gneiss Region, Norway, Dora Maira massif, Piedmont, Italy (coesite-bearing UHP eclogite), Dabie Shan and Sulu, China and Kimberlite xenoliths, Roberts Victor mine, South Africa (diamond-bearing eclogite). Origin affects price, so we name the locality rather than the country on every quote.
Is eclogite hard enough to wear every day?
Yes. At 6-7.5 on the Mohs scale with no cleavage plane, it handles daily wear well. The practical limit is gradual abrasion rather than chipping.
How much does eclogite cost?
Indicatively $10-80 per kilogram for ornamental slabs; diamond-bearing xenoliths from named kimberlites $200-5,000 per specimen. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is eclogite confused with?
Most often Garnet amphibolite, Anyolite (ruby-in-zoisite), Granulite and Dyed composites. A refractive index of 1.67-1.79 (mixed) and a specific gravity near 3.30-3.60 - unusually heavy, which is diagnostic in the hand separate it quickly.
What is eclogite used for besides jewellery?
mineral collecting, decorative objects and architecture and interiors. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for eclogite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about eclogite