Vivid Green Demantoid Garnet on Matrix

Characteristics Demantoid is a variety of andradite garnet, characterized by an intense, emerald-green color, although yellowish-green hues are also found. It is an isometric mineral, typically forming well-developed crystals with dodecahedral or trapezohedral habits. Its name, derived from Dutch, means "diamond-like," referring to its exceptional luster and light dispersion, which even surpasses that of diamond. Physical Properties Demantoid exhibits a Mohs hardness of 6.5-7. Its luster is vitreous to adamantine. The mineral is transparent to translucent. The density of demantoid ranges from 3.85-3.90 g/cm³. Colors and Varieties The typical color of demantoid is emerald green, often with a yellowish tint. The intensity of the green depends on the chromium and iron content. There are no other commercial varieties beyond the name "demantoid" itself, which refers to this specific green variety of andradite. History and Name Demantoid was discovered in the mid-19th century in the Ural Mountains of Russia. The name was given by the Finnish mineralogist Nils Gustaf Nordenskiöld in 1868. It quickly gained popularity in jewelry, especially during the Art Nouveau period, due to its unique brilliance and fire. Uses Demantoid is a prized gemstone, primarily used in jewelry. Its exceptional optical properties make it sought after by collectors and jewelry designers.

Diagnostic features

Identification Demantoid can be identified by its intense, emerald-green color, exceptional luster, and strong light dispersion, which gives it a "fire" similar to diamond. Characteristic inclusions for demantoid are "horsetail" inclusions (byssolite), which are fibrous inclusions arranged radially. Their presence is a strong diagnostic feature. Distinguishing from Similar Minerals Demantoid can be confused with other green gemstones, such as emerald, tsavorite (a variety of grossular garnet), or peridot. It differs from emerald by its lack of cleavage and higher dispersion. It differs from tsavorite and peridot by the presence of "horsetail" inclusions and higher dispersion. A hardness test (6.5-7 on the Mohs scale) can also aid in identification. Crystal Forms Demantoid typically forms well-developed crystals with a rhombic dodecahedral or trapezohedral habit. It can also occur as grains or small aggregates.

Formation environment

Genesis Demantoid forms in metamorphic and metasomatic rocks, especially in serpentinites and skarns, which are products of the alteration of ultramafic rocks. It requires specific geochemical conditions, including the presence of chromium, which is responsible for its green color. Mineral Associations Demantoid often co-occurs with other minerals typical of serpentinite and skarn rocks, such as serpentine, chlorite, magnetite, diopside, calcite, and other garnets. Localities The most famous and historically important demantoid deposits are located in Russia, in the Ural Mountains (Nizhny Tagil region). Other significant localities include Namibia (deposits in the Erongo region), Madagascar, Italy (Val Malenco), and Iran.

For the collector

Quality Criteria The most prized demantoid specimens are those with an intense, emerald-green color, high transparency, and strong "fire." Crystals with a well-developed habit and distinct "horsetail" inclusions are particularly sought after by collectors. The larger and cleaner the stone, the higher its value. Market Prices The prices of demantoids are highly varied and depend on many factors, such as color, clarity, size, the presence of "horsetail" inclusions, and origin. Small, poorly colored stones can cost tens of dollars per carat, while large, high-quality specimens with intense green and distinct inclusions can fetch prices from several hundred to several thousand dollars per carat, or even more for exceptional pieces. Popular Localities The most prized demantoid specimens come from the Russian deposits in the Urals, which are historically known for producing stones of exceptional color and "horsetail" inclusions. Demantoids from Namibia are also highly regarded for their good quality and often larger sizes.