Andradite

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Glassy mostly gemmy green crystals of andradite, this is the variety known as demantoid, measuring to 0.5 cm in size across the front of matrix. This is in good condition. The Antetezambato deposit, located in the Ambanja District of the Diana Region in northern Madagascar, is a world-famous gemstone locality situated along the coast of the Mozambique Channel. Geologically, the deposit is a skarn system formed by the contact metamorphism of Mesozoic calcareous sediments (limestones and marls) by Cenozoic-aged alkaline igneous intrusions. This unique environment led to the formation of high-quality calcium-iron garnets within a weathered mangrove environment, often requiring miners to work in muddy, water-logged conditions. Historically, the deposit was discovered in late 2008, sparking a massive gemstone rush that involved thousands of artisanal miners at its peak in 2009 and 2010. While the most intense period of production was relatively short-lived, spanning from 2009 to roughly 2011, the site remains the premier global source for certain varieties of garnet, with sporadic artisanal activity continuing as local conditions allow. The garnets found at Antetezambato are andradite, with the most prized being the vivid green variety known as demantoid. The green color of these demantoid crystals is attributed to the presence of chromium, and unlike Russian specimens, the Madagascar stones are noted for their exceptional transparency and high refractive index, typically lacking the fibrous horsetail inclusions common in other localities. In addition to the green variety, the andradite at this site occurs in a range of colors, including the yellow to honey-colored variety called topazolite. These andradite crystals are celebrated by collectors for their diamond-like adamantine luster and remarkable fire, which is a result of the high dispersion characteristic of the species, making them some of the most spectacular examples within the broader garnet group.