Mali garnet is the trade designation for a grossular-andradite intermediate species — sometimes termed grandite — discovered in 1994 in the Sandaré region of the Kayes administrative area in western Mali. The find, made by local prospectors in alluvial gravels and later traced to weathered schist horizons, introduced to the international gem trade a garnet whose optical character was unprecedented: a refractive index in the 1.74 to 1.76 range, dispersion approaching 0.057, and a body colour spanning chartreuse, honey-yellow, mint green and warm tan brown.

Chemically, Mali garnets sit on the binary tie-line between grossular (Ca₃Al₂Si₃O₁₂) and andradite (Ca₃Fe₂Si₃O₁₂). Most rough analysed by GIA in the late 1990s and revisited in subsequent Gems & Gemology studies plotted between 65 and 85 percent grossular, the remainder andradite, with trace vanadium and chromium contributing to the green hues and ferric iron driving the yellow-brown range. The presence of andradite is precisely what lifts the dispersion above ordinary grossular and gives faceted material its diamond-like fire under incandescent light.

Optical character

What distinguishes Mali garnet visually is the combination of high lustre, high dispersion and an unusually transparent body. Specimens above five carats are scarce; rough yields tend to be modest because the host material is often included with diopside, calcite and coarse iron-oxide stains. The cleanest stones display a vivid honey or chartreuse colour with strong fire that compares favourably to demantoid, and at certain angles they can mimic the velvet of fine sphene. The relative absence of strong pleochroism — Mali garnet, like all garnets, is singly refractive — means cutters rely on faceting style rather than orientation to maximise return.

Geology and supply

The deposits sit within the Birimian greenstone belt, part of the broader West African craton that also yields the country's gold. Garnet-bearing skarns formed where calc-silicate marbles were intruded by granitic bodies, with later weathering liberating the gem material into surface gravels. Production has been artisanal throughout, controlled by family-based mining cooperatives rather than industrial operations, and supply has been intermittent. The Sandaré pits remained the principal source through the early 2000s; by the mid-2010s output had declined and clean Mali garnet became progressively harder to source, a trajectory documented by the ICA and by dealers reporting at Tucson and Hong Kong shows.

Treatment and identification

Mali garnet is not heat-treated, oiled or otherwise enhanced; the trade has consistently reported the gem as untreated. Identification rests on refractive index, specific gravity (3.65 to 3.77) and the characteristic absorption pattern of ferric iron, alongside a Raman or FTIR fingerprint where available. The visual cue most familiar to gemmologists is the transparent yellow-green body with high lustre, often with healed fissures and rounded mineral inclusions consistent with skarn origin. Confusion with chrysoberyl, sphene and diamond is possible at first glance; refractive index resolves the matter quickly.

Trade and connoisseurship

Mali garnet entered the trade at the precise moment dealers were searching for new garnet varieties beyond demantoid, tsavorite and spessartine. It has never matched those names in volume but has earned a settled place among connoisseurs of the grossular family. Pricing has reflected scarcity rather than fashion; honey-yellow material above three carats with strong fire commands prices comparable to fine spessartine, while green-leaning stones approaching tsavorite hue are rarer and trade at premium levels relative to weight. The Skyjems trade view is that Mali garnet rewards the buyer who values dispersion and a distinctive colour over name recognition; for the collector building a garnet suite, it is essential.