Demantoid Garnet

English Name: Demantoid
Group: Garnet
Variety: Andradite (Calcium Iron Garnet)
Chemical Formula: Ca₃Fe₂(SiO₄)₃
Mohs Hardness: 6.5–7.0
Refractive Index: 1.880–1.889
Dispersion: 0.057
Color: Green to yellowish green, with exceptional fire
Sources: Russia, Italy, Africa, and others

Introduction

Demantoid, the gem variety of andradite garnet (calcium iron garnet), belongs to the garnet family and is a close relative of tsavorite. Its crystals are typically small, usually under one carat. Stones over three carats are considered highly collectible, and those exceeding this size are extremely rare.

The name “Demantoid” is derived from the French word demant, meaning “diamond,” highlighting its diamond-like brilliance.

In May 2008, Christie's Hong Kong auctioned a diamond ring set with a 5.50-carat demantoid from the Ural Mountains of Russia. The piece achieved a final price of HK$1.3 million, demonstrating the gemstone’s exceptional rarity and market value.

Color of Demantoid

Demantoid ranges in color from yellowish green to a vivid green comparable to fine emerald.

Generally, the deeper and more saturated the green, the higher the value. However, lighter yellow-green stones often display stronger dispersion (fire). Whether one prefers intense green color or dazzling fire ultimately depends on personal taste.

Fire and Dispersion

Demantoid is sometimes described as “more brilliant than a diamond” because of its extremely high dispersion value of 0.057—significantly higher than that of a diamond (0.044).

Dispersion refers to the gemstone’s ability to split light into spectral colors, creating what we call “fire.” Due to this remarkable property, demantoid is often cut in a round brilliant style, similar to diamonds, to maximize its sparkle and light performance.

Distinctive Characteristics

Demantoids from the Ural Mountains in Russia are famous for their unique inclusions. Under 10× magnification or a microscope, fine fibrous or needle-like inclusions can be seen radiating outward in curved sprays. These are known as “horsetail” inclusions.

When the horsetail inclusions spread gracefully from a central point—resembling a small flower or even a dandelion—and do not overpower the gem’s brilliance, the stone is considered especially valuable. Well-defined horsetail inclusions are an important identifying and value-enhancing feature of Russian demantoids.

Sources

Demantoid was first discovered in Russia in 1850. Later occurrences were found in Namibia, Italy, Germany, Madagascar, and other regions. However, stones from these localities are often of lower quality and typically lack the characteristic horsetail inclusions.

Demantoids from the Ural Mountains in Russia are regarded as the benchmark for quality, known for stable color, strong fire, and distinctive horsetail inclusions. Their origin remains one of the most important reference points in evaluating this remarkable gemstone.