Demantoid is highly prized by collectors and jewellery enthusiasts for its unique vivid green colour, exceptional brilliance and rarity. This green gemstone is known for its high refractive index and exceptional dispersion, as well as a history tracing back to the mid-19th century.
Demantoid Origin and Formation
Demantoid is a rare and valuable variety of andradite garnet known for its vivid green colour and exceptional brilliance. It was first discovered in Russia in the mid-19th century in the Ural Mountains near the Bobrovka river.
The name “demantoid”, meaning diamond-like, was proposed by Finnish mineralogist Nils Gustaf Nordenskiöld due to the gemstone’s exceptional level of brilliance and fire. The name was readily accepted by mineralogists and jewellers, but it was rejected by the locals. That is the reason why demantoid is also known under such trade names as “Ural chrysolite”, “Bobrovsk emerald”, “Uralian emerald”, and “Syberian chrysolite”.
Demantoid quickly became popular among the Russian aristocracy and was often used in jewellery, including Faberge eggs. However, the supply of demantoid garnet was limited, and it was not until the late 1990s that new deposits were discovered in Namibia and Madagascar.
Demantoid is usually formed in metamorphic rocks. In the case of demantoid garnet, the metamorphic rocks are typically serpentine and talc schist, formed from the alteration of ultramafic rocks such as peridotite. The formation of demantoids requires a specific set of geological conditions. The mineral is created when a high-temperature fluid, rich in silica and other minerals, infiltrates the metamorphic rock and interacts with the garnet precursor mineral, andradite. This interaction causes the andradite to be replaced by demantoid garnet, which grows in the rock as tiny crystals or grains.
Demantoid is a relatively rare gemstone, and the most significant deposits are still found in the Ural Mountains. Other sources of demantoid include Canada, Iran, Italy, Madagascar, Mexico, Namibia and Sri Lanka.
The vibrant green colour of demantoid is one of its most distinctive and sought-after features. The origin of this colour is related to the gemstone’s chemical composition and how it absorbs and reflects light.
Demantoid is a type of garnet that belongs to the andradite group of minerals. It has a complex chemical composition (Ca3Fe2[SiO4]3) and contains trace elements such as chromium and vanadium. These trace elements are responsible for giving demantoid its characteristic green colour.
The specific shade of green in demantoid can vary depending on the amount and type of trace elements present in the gemstone. Most demantoids have a yellowish-green to green colour, with some stones displaying a slightly brownish tint. The most valuable and desirable demantoid garnets have a pure, vivid green colour without any secondary hues.
The colour of the demantoid is also influenced by how it interacts with light. The gemstone has a high refractive index, which means that it bends and reflects light uniquely and strikingly. It also has a high dispersion, which means that it separates white light into its component colours, creating a “rainbow effect” that adds to its overall brilliance.
The intense green colour of demantoid is particularly prized because it is so rare in the world of gemstones. Other green gemstones, such as emerald and tsavorite, are more common but do not possess the same combination of brilliance, fire, and rarity as demantoid garnet. As a result, this gemstone is highly sought after by collectors and jewellery enthusiasts and is often considered a true “collector’s stone.”
Demantoid is generally a relatively clean gemstone, with few inclusions or blemishes visible to the naked eye. However, like all gemstones, it can still have minor inclusions or imperfections, such as tiny crystals, fractures, or other internal or external flaws. These inclusions can affect the gemstone’s clarity and may impact its overall value.
In general, the most valuable and desirable demantoids have a high level of clarity, with few to no visible inclusions or blemishes. Such stones are prized for their vivid green colour and exceptional brilliance, accentuated by their clarity. Demantoids with lower clarity, on the other hand, may have a cloudy or hazy appearance, and their brilliance and fire may be diminished as a result.
The most distinctive feature of demantoids is the “horsetail” value-increasing inclusion present whole or in part in most Russian demantoids. The “horsetail” is referred to as hair-like fibres of chrysotile that radiate outward from a tiny chromite crystal inside the demantoid. Hersetail-included stones are cut in a certain way to highlight the inclusions. If the hair-like fibres are uniform and parallel, the gem may be cut into cabochon to show chatoyancy (cat’s-eye demantoid).
Demantoid Cut and Carat Weight
The cut of demantoid is an important factor in determining its beauty and value. Demantoid is typically cut into round, oval and cushion shapes. Each cut has unique characteristics, and the choice of the cut depends on the size and shape of the rough stone. Some gems with a rare cat’s eye effect or less desirable colouring are cut into cabochons.
In general, demantoids are quite small, with most stones weighing less than 1 carat. Larger stones, such as those weighing over 2 or 3 carats, are exceptionally rare and valuable, especially if they possess good colour, clarity, and cut. Some demantoid garnets have been found that weigh as much as 5 carats or more, but such specimens are exceedingly rare and are highly prized by collectors and connoisseurs.
Demantoid Care and Cleaning
Demantoid is a rare and beautiful gemstone that requires proper care and cleaning to maintain its lustre and beauty over time. Like all gemstones, demantoids can be damaged by scratches, impact, or exposure to chemicals, heat, or light, which is why it is important to follow some care and cleaning guidelines to protect your gemstone investment.
Demantoids can be damaged by exposure to chemicals or harsh household cleaners, so it is best to avoid using these products on your gemstone. Demantoids can be sensitive to temperature changes and sunlight, so it is best to avoid prolonged exposure to these elements.
Clean your demantoid garnet regularly with warm soapy water and a soft brush. Use a mild detergent and warm water to clean your gemstone, and gently brush it with a soft bristle brush to remove any dirt or grime accumulated on the surface. Rinse with clean water and pat dry with a soft cloth. Ultrasonic cleaners are not considered safe for demantoid. It is also recommended to have your demantoid jewellery professionally cleaned and inspected regularly.
To avoid scratches or damage, store your demantoid garnet separately from other jewellery. With proper care, this rare and valuable gemstone can be enjoyed and treasured for generations.
|Colours||Light green, yellowish-green to deep green|
|Hardness||6.5 on the Mohs scale|
|Refractive Index||1.85 - 1.89|
|Transparency||Transparent to opaque|
|Lustre||Vitreous to adamantine|
|Streak||White or none|
Featured image: Dmitrii Stoliarevich / Dreamstime