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 Post subject: Unique colors found in cuprian and some Paraiba tourmaline?
PostPosted: Thu Jul 07, 2022 7:03 am 
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Joined: Thu Sep 25, 2008 10:33 am
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Location: Mars PA
I hesitate to present any limitation on color in tourmaline since I have only seen a lot, but not everything. (I should be seeing an exceptional piece of purple rough from Brazil soon and Nigeria is reported by the GIA to produce a purple hybrid of copper and iron that I would love to see.) That said, I have found cuprian tourmaline to have a level of saturation(purity of color) in the blue-purple range of colors that exceeds that produced by iron (plus manganese). While I think, in theory, iron can produce the same colors as copper in tourmaline, I continue to find the unheated range of cuprian (Paraiba) to be unique to copper-induced color.

Limitations on available colors in the rare blue-purple range of colors come in part from the wholesale heating of almost everything that was produced out of Brazil (Paraiba). Heating Paraiba tourmaline is not simply eliminating the red vector produced by manganese, but it effectively cast purple out of the range of colors define as Paraiba colors. The treatment of Mozambique material has not been as universal, but the rewards for successfully heating purple cuprian to highly valued blue-greens are substantial.

If you can hold on to any blue purple tourmaline, you may be blessed with some of the rarest colors in tourmaline, whether it comes from iron or copper.

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 Post subject: Re: Unique colors found in cuprian and some Paraiba tourmali
PostPosted: Mon Jul 11, 2022 1:37 pm 
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Related Article:
Copper-bearing tourmaline, also known as Paraiba-type tourmaline (or Paraiba tourmaline; LMHC 2012), is one of the most sought-after and appreciated coloured stones in the trade. This is mostly due to its vivid colour, which in the best cases is described as ‘neon’ or ‘electric’ blue. However, Cu-bearing tourmalines are found in many colours, ranging from saturated blue (sapphire-like colour) to vivid and light blue, greenish blue to bluish green, green, and even greenish yellow and purple.

Interestingly, Cu-free indicolite tourmaline with Fe2+ as a chromophore can sometimes show a greenish blue colour very similar to that of Paraíba-type tourmaline. This material is often marketed as Lagoon tourmaline and is known, for example, from Namibia and Afghanistan.

The separation of non-Cu-bearing indicolite from Paraíba-type tourmaline is usually straightforward. However, the situation becomes more complex when stones contain both Cu and Fe. This recently published short article by Dr. Michael Krzemnicki and Dr. Hao Wang in the Journal of Gemmology elaborates on these research questions.

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