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Tranomaro grandidierite mine

Faceted Tranomaro grandidierite, one of the very few gem-quality stones of this kind
Faceted Tranomaro grandidierite, one of the very few gem-quality stones of this kind./ American-thai, Wikimedia Commons / CC BY-SA 4.0

WorldBlue  In short

The only notable find of gem-quality grandidierites in the world is a remote, little known location in the southern Madagascar. Tranomaro grandidierite mine was discovered in May 2014.

2.8 out of 10 stars 28.3%

GPS coordinates
24.603 S 46.4756 E
Location, address
Africa, Madagascar, Anosy Region, Province de Toliara, some 15 km from Tranomaro village in unknown direction. Coordinates show Tranomaro village.
Gemstones
Grandidierite

Map of the site

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WorldYellow In detail

Description of grandidierite

Grandidierite from Cap Andrahomana, Madagascar
Grandidierite from Cap Andrahomana, Madagascar. / Robert M. Lavinsky, Wikimedia Commons / CC BY-SA 3.0

French mineralogist Alfred Lacroix discovered grandidierite in 1902 in the seaside cliffs of Cap Andrahomana, southern Madagascar. Later, in 1960, no more grandidierite was found in this site.

He named the mineral after a French explorer Alfred Grandidier (1836-1921).

Grandidierite is a bluish-green stone which is well suited to be a gemstone:

  • It has a rare, interesting color. Most of the blue-colored gemstones are artificially “improved” by heating or chemicals, but grandidierite has a naturally intense color.
  • The stone is hard: 7.5 by Mohs scale – harder than quartz and a lot harder than, for example, glass.
  • It has a strong pleochroism: when turning a transparent stone, it changes the color from colorless or pale yellow to blue-green, and then to neon blue. This is an interesting feature but it makes the life of a jeweler a lot harder: craftsmen should plan well the faceting of the stone to show the beautiful blue-green color.
  • One characteristic, though, makes it harder to process: the stone has a well-expressed cleavage, e.g. it divides along specific planes irrespective of the wishes of the jeweler. Due to this: if you are one of the few persons on the planet who can touch a grandidierite jewel, be careful and do not drop the stone, it may break up. That would be a huge loss!

Even opaque pieces of grandidierite that are not gemstones, are very rare. The stone is found in small quantities in Algeria, Antarctica, Canada, New Zealand, the USA (New York, Wyoming), India, and some more countries.

It is estimated that one out of 10,000 pieces of grandidierite is a true gem.

Tranomaro grandidierite

In May 2014 there was discovered a find of transparent, gem-quality crystals of grandidierite near Tranomaro. Stones were found in a weathered pegmatite with two grandidierite veins. Before this just a few totally transparent pieces of grandidierite were found in Sri Lanka and also in the southern Madagascar, Cap Andrahomana.

Tranomaro grandidierite is mined with simple methods: up to 15 m deep pits. The area is not safe for travelers: there are reported attacks by gangs. The mine is not accessible by car.

Until March 2016 there were mined some 800 kg of grandidierite. This is an unusually large quantity! But only 60 g or 300 carats (!) of this mass were transparent gems!

Nevertheless, nice crystals of translucent grandidierite there were up to 15 cm long and 930 g in weight.

Too rare for market?

The largest known grandidierite gemstone is 78 carats large, owned by Joseph Fam, Singapore. This is a faceted stone, but it is not entirely transparent but rather translucent.

In Wilensky Gallery (New York, USA) in 2019 were presented three wonderful crystals from Tranomaro, respectively 2.86, 3.14, and 4.96 carats large. Their price was, respectively, 69, 78, and 129.5 thousand USD. These are not the most expensive gemstones in the world but are not very far from the most expensive ones. In fact, before the discovery of the Tranomaro grandidierite, the very first known piece of transparent grandidierite was sold for 50 thousand USD in 2003, although it weighs only 0.29 carats. This stone was found in Sri Lanka.

In general, it is assumed that there simply is no market and no set price for these stones because they are too rare and deals are too few.

Mineralogically similar to grandidierite, but even more rare is another gemstone: ominelite. There is only one find of gem quality stones of this kind: Misen River ominelite find in Japan.

 

References

  1. Delphine Bruyère, Claude Delor, Julien Raoul, Rufin Rakotondranaivo, Guillaume Wille, Nicolas Maubec, and Abdeltif Lahfid, A New Deposit of Gem-Quality Grandidierite in Madagascar. Gems&Gemology, Fall 2016, Vol. 52, No. 3, page accessed on the 24th July 2022.
  2. Wim Vertriest, Stanislas Detroyat, Supharart Sangsawong, Victoria Raynaud, and Vincent Pardieu, Grandidierite from Madagascar. Gems&Gemology, Winter 2015, Vol. 51, No. 4, page accessed on the 24th July 2022.
  3. Brecken Branstrator, 5 Things to Know About … Grandidierite. National Jeweler, April 008, 2019. Page accessed on the 24th July 2022.

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