Antsongombato gem mine, Antsentsindrano, Anosiarivo Manapa, Betafo, Vakinankaratra, Madagascar

The mine was opened in 1998, work stopped in October 2000 for safety concerns after the mining operation of the londonite-bearing pegmatite reached a depth of more than 40 meters. White to gray marble, a number of sub-parallel pegmatitic dikes, parallel with the metamorphic foliation, outcrop over a distance of about 600 m. The dikes are normally a few decimeters wide but locally can be over 2 m wide and up to 300 m long. Only one dike produces abundant and well-formed crystals of londonite. Others contain low quality rhodizite-londonite crystals. Londonite crystals are concentrated at the core of the dike, even in very narrow portions (a few centimeters) of the pegmatite.

The londonite crystals are normally hosted in K-feldspar, albite and quartz, but in some cases they are hosted in danburite, pollucite and red tourmaline. Crystals in miarolitic cavities are very rare, and normally, they are of high quality.

The best londonite crystals recovered at the mine had deep-yellow colour with local gemmy portions. The average size of the crystals is between 0.5 to 2 cm across. Large crystals are exceptional as very few are over 6 cm. Cut gemstones are generally small, but are, in some cases, over 1.5 carats.

Madagascar, extraLapis English No.1, 2001, pp. 70 - 72

Gemstone List

Gemstones from Antsongombato gem mine, Antsentsindrano, Anosiarivo Manapa, Betafo, Vakinankaratra, Madagascar by Colour

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