Golden brown, brilliant-cut andradite, 3.07 cts, 8.9 mm, Mexico. Photo courtesy of liveauctioneers.com and Heritage Auctions.
Andradite is one of the most sought after garnet species. Although more sources have been discovered in recent decades, gem-quality andradites remain rare.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Demantoid garnet, the chromium-bearing, green variety of andradite, is the most well-known and valuable andradite. For more information on value and quality factors for this gem, consult our demantoid buying guide.
Round brilliant-cut demantoid with horsetail inclusions, 0.87 cts, 5.7 mm, Russia. © The Gem Trader. Used with permission.
For more information on value and quality factors for andradites and other garnets in general, consult our garnet buying guide.
Round andradite garnet, 6.06 cts, 11.4 x 11.43 x 6.87 mm. Photo courtesy of liveauctioneers.com and Heritage Auctions.
| Data | Value |
|---|---|
| Name | Andradite |
| Is a Variety of | Garnet |
| Varieties | Demantoid Garnet, Melanite, Topazolite |
| Crystallography | Isometric |
| Refractive Index | 1.855-1.95 |
| Colors | Green, yellowish green, yellow, brown, brownish red, black. May rarely show color zoning. |
| Luster | Vitreous to resinous |
| Hardness | 6.5-7 |
| Fracture | Conchoidal |
| Specific Gravity | 3.70-4.10; melanite about 3.9; demantoid 3.82-3.88. |
| Birefringence | None |
| Cleavage | None |
| Dispersion | 0.057 |
| Heat Sensitivity | Some |
| Luminescence | None |
| Luminescence Present | No |
| Enhancements | Heat (demantoid) |
| Typical Treatments | Heat Treatment |
| Transparency | Translucent to transparent |
| Absorption Spectrum | A strong band is visible at 4430, cutoff at the violet end of the spectrum. Sometimes (in demantoids) the Cr spectrum is visible, with a doublet at 7010, sharp line at 6930, and 2 bands in the orange at 6400 and 6220. Demantoid is red in the Chelsea filter. |
| Phenomena | Chatoyancy, iridescence (rare for andradites); color change (rare for andradite-grossular series garnets). |
| Birthstone | January |
| Formula | Ca3Fe2Si3O12 |
| Pleochroism | None |
| Optics | Isotropic, may show anomalous birefringence. N = 1.88-1.94; demantoid: 1.881-1.888; topazolite (yellow): 1.887; melanite: 1.89. |
| Etymology | Andradite is named after the Brazilian mineralogist, José Bonifácio de Andrada e Silva, who described one of the sub-varieties of this garnet species. “Colophonite” comes from its resemblance to colophony or rosin, a plant resin. “Demantoid” comes from the old German demant for “diamond,” due to its high dispersion. “Melanite” comes from the Greek melanos for “black.” Topazolite is named after its resemblance to yellow topaz. |
| Occurrence | Andradite occurs in schists and serpentine rocks (demantoid and topazolite); also in alkali-rich igneous rocks (melanite); and in metamorphosed limestones and contact zones (brown and green colors). |
| Inclusions | So-called horsetail inclusions of byssolite (fibrous amphibole) or chrysotile (see “Identifying Characteristics” below). Curved fibers (not necessarily “horsetails”), single-phase (hollow tubes) and two-phase inclusions, fingerprints, crystals. |
Andradites: California (melanite, 5.9) // Russia (demantoid, 0.6); Korea (0.95); Italy (0.90). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Andradites have a higher dispersion than any other variety of garnet. It even exceeds that of other well-known jewelry stones, such as diamonds. While dark body colors may mask their “fire,” light colors, especially in small gems, can be dazzling.
Andradites can occur in a wide range of colors: green, yellowish green, yellow, brown, brownish red, and black. While rare, color zoning may occur, such as red/brown, brown/orange/green, and even red/green.
This unusual garnet is definitely an andradite but it’s bi-colored green and red. For more information on this particular gemstone and its GIA analysis, see this article. 2.71 cts, emerald cut. © All That Glitters. Used with permission.
The following are the andradite varieties and series most likely to be encountered either as faceted gems or mineral displays.
The most well-known andradite variety, demantoids can combine rich, emerald-like green color with exceptional dispersion and brilliance. They receive their green color from chromium (Cr) traces, while ferric iron (Fe3+) traces may add yellow color. These rare gems are always in high demand and may be the most valuable of any garnet variety.
See our separate demantoid garnet gem listing for more information.
These yellow to yellowish green andradites are even rarer than demantoids, especially as facetable material. As a result, they’re less well-known and encountered more rarely in jewelry.
Matched topazolite garnets, 1.19 ctw, 5.1 mm, round brilliant cuts, Russia. © The Gem Trader. Used with permission.
The name refers only to a color similarity with classic yellow topaz. Of course, garnets and topazes are distinct gem species.
Large (up to 3.5 cm across), olive-green to cognac-colored topazolite garnets in matrix, Antetezambato, Ambanja District, Diana Region, Antsiranana Province, Madagascar. © Rob Lavinsky, www.iRocks.com. Used with permission.
These andradites contain 1-5% titanium oxide and have black color. They can show a near adamantine (diamond-like) surface luster, thus making them very reflective.
Melanite crystal, 2.4 x 2.2 x 1.9 cm, Chihuahua, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.
Historically, melanites have been used for mourning jewelry. They also make fine accent stones.
Sterling silver ring with a gray pearl, cubic zirconias, and melanites. The melanites measure 1.55 mm each. Photo courtesy of liveauctioneers.com and Jasper52.
Andradites with strong, multi-colored iridescence have been found in Mexico, the southwestern United States, and Japan. This material, especially that from Japan, has been called “rainbow garnet.”
Iridescent andradite garnet, freeform cabochon, 10.9 x 8.9 mm. Japan. © The Gem Trader. Used with permission.
This granular variety of andradite, usually brown, reddish, or orangish, has a resinous, amber-like luster.
Mali garnets are a blend of andradite and grossular species. They show dispersion and colors like andradites but have somewhat greater wearability, with a higher hardness and no heat sensitivity.
Pear-cut Mali garnet, 1.46 cts, treated gem. Photo courtesy of liveauctioneers.com and Collector’s Liquidation.
Some Mali garnets may show a color change effect, from grayish green in fluorescent light to brown in incandescent light.
Schorlomite, a titanium-rich variety of garnet (N = 1.935), can form a series with andradite, which creates dark-colored stones, generally black, brown, or reddish brown. Like melanite, schorlomite occurs in alkali-rich igneous rocks.
The golden horsetail inclusions of demantoid garnets are some of the most well-known and celebrated variety of gemstone inclusions. Gem collectors and jewelry aficionados prize them so much that gem cutters may even facet these stones to feature them. These inclusions may also cause a cat’s eye effect in some stones.
Horsetails have long been considered diagnostic for identifying demantoids. However, a 2018 study found horsetail inclusions in non-demantoid (brown) andradite. Thus, horsetails may not be sufficient in and of themselves for identifying demantoids.
This closeup of a Russian demantoid shows horsetail inclusions spreading from a chromite crystal within the gem. © The Gem Trader. Used with permission.
Many varieties of garnets show colors like those of andradites, and most garnets contain blends of multiple species. Therefore, distinguishing garnet varieties can be difficult. This chart comparing the refractive indices (RI), range of colors, and absorption spectra of different garnet species may help.
Uvarovites and tsavorites have demantoid-like (or emerald-like) green color. However, the specific gravity (SG) of demantoid exceeds that of these other rare and deep-green garnets.
Scientists have synthesized andradites for research into their physical and optical properties, such as their heat capacity and optical absorption. However, there’s no known jewelry use for this lab-created material.
Demantoid garnets may receive heat treatments to lighten their color and remove brown tones.
There are many sources of andradite across the globe, but gem-quality supplies are limited.
In 2009, a mine near Antetezambato, Madagascar emerged as a notable source of fine, gem-quality demantoid and topazolite.
Andradite crystal on matrix. Antetezambato, Ambanja District, Diana (Northern) Region, Antsiranana Province, Madagascar. Photo by Géry Parent. Licensed under CC By-SA 3.0.
Russia has produced fine demantoids as well as topazolites and some (small) brown andradites.
Italy produces many varieties of andradite. Ala, Piedmont, yields dark apple-green demantoids and yellow to yellowish green topazolites. Val Malenco, Sondrio Province is also a notable source of demantoid. Monte Somma, Vesuvius, and Trentino produce melanite.
In the United States, San Benito County, California has produced a variety of gem-quality andradites: topazolite (N = 1.855-1.877, SG = 3.77-3.81), demantoid (N = 1.882, SG = 3.81), melanite, and an unusual cat’s eye material. Other US sources include the following: Arizona; Arkansas; Colorado; New Jersey; New Mexico (in metamorphic limestones and ore deposits); Pennsylvania.
Andradite garnet: Stanley Butte, Arizona (ca 3 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Other notable sources include the following:
Andradites on matrix, up to 1” thick, Rosario Mabel claim, Pampa Blanca, Castrovirreyna Province, Huancavelica Dept., Peru. © Rob Lavinsky, www.iRocks.com. Used with permission.
Russia holds many fine demantoids in museum collections.
A collector in California owns a huge, green topazolite crystal, around 1 ounce in weight, that would yield faceted gems over 20 carats.
Like most garnets, andradites makes good jewelry stones, especially for engagement rings. However, most garnets are also heat sensitive, and andradites can contain crystal and liquid inclusions as well. Therefore, never clean them with ultrasonic cleaners or steamers since the stones may shatter. Instead, use warm water, mild detergent, and a soft brush.
Some andradites may have a hardness of 6.5, which means they are somewhat susceptible to scratching. Use protective settings for these gems.
For more recommendations, consult our gemstone jewelry care guide.
Grayish yellow-green andradite garnet, oval modified brilliant cut, 1.94 cts, 8.46 x 6.43 x 4.38 mm. Photo courtesy of liveauctioneers.com and Dan Morphy Auctions.
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