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Alain.R.Truong
21 avril 2012

Large gem Tanzanite crystal, Merelani Hills, Umba Valley, Lelatema Mts, Arusha Region, Tanzania

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Large gem  Tanzanite crystal, Merelani Hills, Umba Valley, Lelatema Mts, Arusha Region, Tanzania. photo Heritage Auctions

Tanzanite: one of the most talked-about 'new' gemstones of the last couple of decades is, with very minor exceptions, a 'one locality' gemstone. This lot consists of a single, large gem crystal of Tanzanite in its uncut and untreated condition. Such things are offered only rarely on the open market. There are a couple of very good reasons: 1. Not that many big crystals are recovered in the mines to begin with; and 2. If there were any gem material in such a crystal, its next appearance would normally be as a cut stone in a piece of jewelry. The operators of the Tanzanite mines know that they can get more return on their investment, in a shorter time, by cutting up any fine, large crystals that they find. This means, because of its intrinsic value as gem rough, very few large and undamaged specimens escape an appointment with a faceting machine. This one got away.

A sublime example of the marriage of color and form, this gem Tanzanite crystal is over FOUR INCHES in height with deep, saturated color and no heat treatment - which is unusual by itself. As a result, the rarely seen "third color": a warm peach color shading into red is still detectable when viewed from one direction. In order to demonstrate this variable color phenomenon, several photos of this crystal were taken using a polarizing filter, similar to those in sunglasses. Since 'normal' light is a mix of light rays with different polarization angles, by rotating a polarizing filter in front of the camera lens, you can observe the separate color components that together, account for the unique appearance of Tanzanite. Each of the colors in the second photograph can actually be observed in real life by viewing the crystal from different directions. This photo shows all of the colors that make up what WE see as "Tanzanite".

The exterior of this gem prism is brilliantly lustrous with none of the nicks and flaws that often accompany most rough Tanzanite crystals. It measures 4 1/8 x 1 7/8 x ¾ inches (10.5 x 4.8 x 1.9 cm), and has a custom base. It is in pristine condition. Lot 49053. Estimate: $300,000 - $350,000.

Provenance: Private European collection    

Heritage Auctions. 2012 May 20 Natural History Signature Auction- New York 

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