Demantoid
Garnet group · also called Demantoid garnet, Green andradite
Demantoid is the green, chromium-coloured variety of andradite garnet. Its dispersion of 0.057 exceeds diamond's, giving it more fire than any other common gemstone, and its refractive index sits above the range of a standard refractometer. Russian material may contain the horsetail inclusion that no other source produces.
What is demantoid?
Demantoid is the green, chromium-coloured variety of andradite garnet, one of the rarest and most optically remarkable stones in commerce. Its dispersion of 0.057 exceeds diamond's, its refractive index sits above the range of a standard refractometer, and Russian material may contain a diagnostic inclusion found nowhere else on earth.
The species is andradite, calcium iron silicate. Demantoid is the trade name reserved for transparent green material; yellow andradite is called topazolite and black andradite melanite, and neither commands anything like the same price. Chromium supplies the green, and iron — an essential part of the formula rather than an impurity — supplies a yellow component that pushes many stones toward olive.
What gives demantoid its colour and its fire?
The green comes from chromium substituting into the structure, the same ion that colours emerald and ruby. Iron is present in every andradite by definition and contributes a yellowish cast, so the purest greens occur where chromium is high and the iron contribution is masked.
The fire is separate from the colour and comes from the crystal structure itself. Demantoid disperses white light into its component colours at a rate of 0.057, against 0.044 for diamond and 0.017 for sapphire. In practice this means coloured flashes of a strength you will not see in any other coloured stone.
The two properties compete. A deeply saturated green body colour absorbs much of the dispersed light before it escapes, so the fire is swallowed. A pale stone shows the fire clearly but has little colour to sell. The most admired demantoid sits deliberately in the middle, and this is why cutting matters more here than in most species: a well-proportioned two-carat stone will outperform a badly cut four-carat one on the only two qualities anyone is paying for.
How is demantoid identified?
The first test is a negative one. At 1.880 to 1.889 demantoid reads above the limit of a standard refractometer, which tops out near 1.81. The instrument shows a blank field, and that blank is itself informative, because very few green gemstones read over the limit.
Specific gravity confirms it. At 3.81 to 3.87 demantoid is heavy, distinctly heavier than tourmaline at 3.06 or than emerald at 2.71. A hydrostatic balance separates it from every common green stone in a couple of minutes.
The third check is optical character. Demantoid is cubic, therefore singly refractive: no birefringence, no doubling of facet edges, no pleochroism. That alone excludes green tourmaline, peridot, diopside and epidote, all of which are strongly doubly refractive.
Against tsavorite, the other cubic green garnet, the separation is straightforward once you have the numbers: tsavorite reads 1.734 to 1.745 with a specific gravity of 3.57 to 3.65, both comfortably within instrument range, and it shows almost no fire.
What is a horsetail inclusion?
Russian demantoid frequently contains horsetails — sprays of fine, radiating fibres of chrysotile or byssolite curving outward from a central point, resembling the tail of a horse in motion.
They are among the very few inclusions in gemmology that carry an origin conclusion on their own. No other locality has produced them in this form, so a clear horsetail is treated by laboratories as evidence of Ural origin. It is also the rare case where an inclusion raises value rather than lowering it, because Russian origin commands a premium and buyers actively seek the feature.
The reverse does not hold. Namibian material from the Green Dragon mine is typically cleaner and often more saturated, and contains no horsetails at all, so their absence proves nothing about origin. This asymmetry is worth remembering: a horsetail is evidence, an empty stone is not.
Is demantoid treated?
Frequently, and the honest answer depends on where it came from.
Heating to remove a brownish component and improve the green is common in African and Madagascan material. Temperatures are moderate, the change is stable and permanent, and it should be disclosed. Russian material is more often untreated, partly because it needs less help and partly because the market punishes treatment more heavily where the origin premium is largest.
Nothing else is routinely done. Demantoid is not oiled, not fracture-filled and not diffused, so the disclosure question is a single one: heated or not. Ask it directly, and expect the price difference to be real rather than notional.
Where does demantoid come from?
Russia remains the reference. The Ural deposits at Bobrovka and Poldnevaya have been worked intermittently since the 1850s and have never produced in quantity. Stones are usually small, often included, and carry the horsetails.
Namibia — the Green Dragon mine in the Erongo region, from the 1990s — produces cleaner and more strongly coloured material with a slightly different chemistry and no horsetails. For many buyers it is optically the better stone; it simply lacks the name.
Madagascar produced a large and short-lived flood from Antetezambato beginning in 2009. Much of that material was heated, and the deposit's rapid rise and fall depressed prices for a period before supply thinned again.
Iran, in Kerman province, and Italy, in Val Malenco, contribute small quantities, the latter mostly to collectors rather than to the trade.
Where the name comes from
Demantoid entered the trade after the Ural discovery of the mid-nineteenth century, taking its name from the Dutch *demant*, meaning diamond — a reference to the fire rather than to any resemblance in colour.
Its reputation was made in Russia rather than in the mines. Fabergé used it extensively in the decades before 1917, and the association with the Russian court gave the stone a standing far above what a garnet would otherwise command. When the workshops closed, the material largely disappeared from Western commerce for most of a century, which is why fine antique pieces set with demantoid are so often the first ones a collector sees.
What sizes are available?
Small ones, mostly. Demantoid above two carats is uncommon from every source, above five carats it is a collector's stone, and above ten it is a named piece with a history.
The consequence for a buyer is that the price curve steepens far more sharply with weight than in most species. A fine three-carat demantoid may cost several times the per-carat price of a fine one-carat, where in a more abundant gem the difference would be modest. If you need a matched pair, or a suite, expect a wait measured in months and expect to pay a premium for the matching itself.
How much is demantoid worth?
Origin sets the top of the range. Russian stones with visible horsetails and a laboratory report confirming Ural origin command the highest prices of any garnet. Namibian material of comparable appearance sells for meaningfully less, and heated Madagascan goods lower again.
After origin, in order: the balance between colour and fire, then clarity, then size — with size mattering more above two carats than below. A brownish cast is the most common reason a demantoid is cheap, and it is easy to miss under warm shop lighting.
Because the origin premium is large and depends on a single inclusion type, this is a stone where a report earns its cost quickly on anything above a carat or two.
Is demantoid durable enough to wear?
At 6.5 to 7 on the Mohs scale, demantoid sits at the soft end for a stone worn daily. Airborne dust contains quartz at hardness 7, which means a ring stone in constant wear will lose polish over years — not dramatically, but visibly.
It has no cleavage, so it is not fragile in the way topaz or kunzite are: the risk is abrasion rather than breakage. That makes it well suited to earrings, pendants and occasional-wear rings, and acceptable in a daily ring if the setting protects the girdle.
Clean it with warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on included stones, and avoid steam entirely.
How to buy demantoid without being caught out
Judge the stone under a point light source, not diffuse lighting. Fire is the property you are paying a premium for, and it simply does not appear under a softbox or an overcast window — which is exactly why some sellers photograph it that way.
Look for the brown before you look for anything else. Then put a loupe on it before you ask the price: horsetails change what you are holding, and a seller who has not noticed them may not have priced them in.
Above a carat or two, commission a report that states origin and heat treatment. And treat a stone described as Russian without a report as Namibian for pricing purposes — the premium is large enough that the claim needs support, and in this trade an unsupported origin claim is the most common way money is lost.
See our gems, or tell us what you are looking for.
Does demantoid really have more fire than diamond?
Yes, measurably. Demantoid disperses light at 0.057 against diamond's 0.044, separating white light into coloured flashes more strongly. Whether you see it depends on the stone: a deeply saturated green body colour absorbs much of the effect, so the finest examples are cut in a medium tone.
What is a horsetail inclusion?
A spray of fine radiating fibres of chrysotile or byssolite curving out from a central point inside the stone. It occurs in Russian Ural demantoid and essentially nowhere else, so it is treated as evidence of origin — and it raises value rather than lowering it, which is very unusual for an inclusion.
Why does demantoid not read on a refractometer?
Its refractive index of 1.880 to 1.889 sits above the roughly 1.81 limit of a standard refractometer, so the instrument shows a blank field. That blank is itself useful information, since very few green gemstones read over the limit. Confirm with specific gravity and the absence of double refraction.
Is demantoid hard enough for a ring?
It is on the soft side. At 6.5 to 7 on the Mohs scale it will abrade over years of daily wear, since airborne dust contains quartz at hardness 7. It suits earrings, pendants and occasional-wear rings, and in a ring the girdle should be protected by the setting.
Is demantoid treated?
Often, in African and Madagascan material, where heating removes a brownish component and improves the green. The change is stable and should be disclosed. Russian material is more commonly untreated, and the price difference between heated and unheated is real enough to ask about explicitly.
How much does demantoid cost per carat?
It varies by origin more than almost any other garnet. Russian stones with horsetails and a report command the highest prices, Namibian material sells for meaningfully less at similar appearance, and heated Madagascan goods lower again. Above two carats the curve steepens sharply in every origin.
Demantoid available now
Nothing in demantoid is listed at the moment. We buy continuously — tell us the colour, the weight range and the budget and we will come back when something matches.
Send a briefLooking to buy demantoid? See the collection, the rough, or send us a brief.