Andradite

specimen number:
2262030

location:
Antetezambato Mine, Antsakoamanondro, Ambanja, Diana, Madagascar

description:
Partly gemmy attractive lustrous green crystals of andradite measuring to 1.0 cm in size across the top of matrix. This is the variety often called demantoid. In good condition. A choice thumbnail.

The Antetezambato demantoid deposit, located in the Ambanja District of northern Madagascar, is a world-class locality discovered in 2009 that redefined the market for andradite garnet. Geologically, the deposit is a contact metasomatic skarn formed where Cenozoic-aged igneous intrusions interacted with Mesozoic calcareous sediments. This process led to the formation of brilliant green andradite crystals, known as demantoid, within cavities and fractures of the altered limestone. The crystals are prized for their high dispersion and range from vivid emerald green to yellowish-green hues. Historically, the site experienced a massive rush shortly after its discovery, with thousands of artisanal miners working the mangroves and coastal sediments between 2009 and 2011. While the initial surface-level boom has subsided, controlled mining continues to produce high-quality specimens and gemstones. This locality is unique because, unlike Russian demantoids which typically contain horsetail inclusions of chrysotile, the Antetezambato specimens are often internally clean or contain distinct inclusions characteristic of a skarn environment.

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