Demantoid Garnet Buying Guide


Demantoid garnet buying guide - 0.73 ct Russian Demantoid and diamond ring
This 18k gold ring features a 0.73-ct oval step-cut Russian demantoid, accented with 44 D-grade flawless diamonds. By courtesy of KAT FLORENCE.

Stunning green hues and a brilliance that outshines diamond combine to make demantoids truly captivating. This variety of garnet is an entirely different stone than the more familiar dark red gems of the garnet family. In fact, demantoid garnets are much rarer than the red varieties and are the most valuable type. Although named demantoid, or “diamond-like,” these garnets actually exceed diamonds in both brilliance and dispersion. Their horsetail inclusions are a delight to collectors, too.

Before your next demantoid garnet buying trip, read up on what makes this variety of the January birthstone unique and the quality factors that most impact cost.

Demantoid Garnet Buying and the Four Cs

The IGS garnet value listing has price guidelines for demantoid garnet. Learn to identify the different species of garnet.

Color

Demantoid is the green variety of andradite garnet, with colors ranging from deep forest greens to light, nearly colorless hues. For this variety, the connoisseur’s most important consideration is the trade-off between depth of color and visible brilliance.

demantoid garnet buying guide - tagil demantoid 1.37 ct
Bright, well-saturated green hues in this 1.37-ct gem from the Ural Mountains make it a prized specimen. © Ildar Latypov Minerals. Used with permission.

While demantoid has a higher dispersion than diamond, darker tones may obscure this effect. Still, medium-dark tones hold the highest value, where the green color is strongest. For those who prefer greater dispersion, a slightly lighter gem will sparkle strongly without much loss of color.

Yellow secondary hues are often present and detract from the gem’s price. Gems with low saturation will appear more brown.

demantoid garnet buying - olive green mineral specimen
This demantoid specimen from Madagascar is olive green to brown and toes the line between demantoid and topazolite, the yellow variety of andradite. © Rob Lavinsky, www.iRocks.com. Used with permission.

Clarity

Although high clarity is always desirable, some connoisseurs and mineral enthusiasts will delight in the horsetails frequently present in demantoid garnets. These fibrous inclusions are usually yellow or golden in color and emanate from the center of the stone, curving outward. When present, a horsetail inclusion is a diagnostic indicator of demantoid garnet. However, not all demantoid garnets will display a horsetail.

Overall, clarity doesn’t have a high impact on demantoid pricing. Both eye-clean gems and gems with prominent horsetail inclusions will command slightly higher prices than gems with other inclusions.

demantoid garnet buying guide - horsetail inclusion
Magnified view of a horsetail inclusion. © Ildar Latypov Minerals. Used with permission.

Cut

Garnets are available in nearly every cut. Still, demantoid’s high dispersion means the gem typically holds the most value in a round brilliant cut. Small demantoids should always have good cuts with the correct proportions. Lapidaries may cut larger specimens to retain more weight.

0.85-ct stone with thin cuts to create reflective lines. © Ildar Latypov Minerals. Used with permission.

Carat

Like other green varieties of garnet, demantoid is rare in any size and especially rare in large sizes. Stones under one carat are readily available, but any gem above 3 carats is a collector’s item. Thus, price per carat increases rapidly for this gem.

demantoid garnet buying guide - 76 carat color zoned rough
This color-zoned demantoid garnet from the Ural Mountains near Poldnevaya weighs a whopping 76 carats rough. © Ildar Latypov Minerals. Used with permission.

Sources of Demantoid Garnet

Demantoid garnets were discovered in 1853 in the Ural region of Russia, and the Ural Mountains remain an important source for demantoid. Some collectors will pay a premium for stones from this locale. Other sources include Pakistan, Sri Lanka, Italy, Namibia, and Madagascar.

Jewelry Considerations

At 6.5 on the Mohs scale, demantoids are fairly resistant to scratching, but dust may still scratch this stone. Still, with no cleavage, demantoid garnets are less prone to breaking than other jewelry stones. Thus, demantoid’s high durability makes it a great gem for any type of setting.

demantoid garnet buying guide - padparadscha and demantoid ring
This Edwardian style ring features a 2.97-ct unheated padparadscha sapphire with two African demantoid garnet side stones of 1.12 carats each. With these durable gems, the ring is sure to last. © J. Grahl Design. Used with permission.

Demantoid Garnet Buying and Heat Treatment

Low-temperature heat treatment under a reducing atmosphere lightens the tone of some very dark specimens and may remove brown hues. This treatment mimics natural heating that some deposits have already undergone. It produces a stable color. Laboratories cannot reliably detect this treatment, but some may note whether there is evidence of heat treatment. Because of the resulting color’s stability, this treatment is largely accepted and doesn’t heavily impact price.

Demantoid Garnet Simulants

Green glass or green synthetic yttrium aluminum garnet (YAG) can simulate demantoid garnet. However, consumers won’t commonly encounter these imitations.

About the author
Addison Rice
A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club. When she isn't writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
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