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 Post subject: Re: Stone(s) of the Day
PostPosted: Tue May 21, 2019 9:06 am 
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Joined: Mon May 20, 2019 3:47 pm
Posts: 36
Stone: Grandidierite
Weight: 270ct or 54grams
Origin: Madagascar
Crystal: Rough Specimen



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Last edited by offimatrix on Wed May 22, 2019 1:18 pm, edited 1 time in total.
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 Post subject: Grandidierite
PostPosted: Tue May 21, 2019 1:11 pm 
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Joined: Sun Oct 16, 2005 12:22 pm
Posts: 19943
Location: San Francisco
Quote:
A New Deposit of Gem-Quality Grandidierite in Madagascar
Delphine Bruyère, Claude Delor, Julien Raoul, Rufin Rakotondranaivo, Guillaume Wille, Nicolas Maubec, and Abdeltif Lahfid
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ABSTRACT
A new deposit of grandidierite, considered one of the world’s rarest gems, has been discovered in southern Madagascar. The new deposit is outside the town of Tranomaro, near the original locality of Andrahomana. It occurs in the form of strong bluish green to greenish blue translucent to transparent crystals measuring up to 15 × 7 × 3 cm. Grandidierite is the magnesium end member in the solid-solution series with ominelite as the iron end member. The studied samples have a very low Fe/(Mg + Fe) ratio. This confirms that the Tranomaro deposit, together with Johnsburg in New York State, provides the purest grandidierite ever found. The crystals host inclusions of Cl-apatite, zircon, and monazite. The paragenesis also includes plagioclase, phlogopite, enstatite, diopside, dravite, and sapphirine (locally as gem-quality crystals). Transparent crystals have been faceted, yielding small but eye-clean jewelry-quality gems.
Read full article here


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