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SSEF conducts analysis of cobalt-blue spinel from new source
https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=91&t=26465
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Author:  Barbra Voltaire, FGG [ Fri May 20, 2022 12:46 pm ]
Post subject:  SSEF conducts analysis of cobalt-blue spinel from new source

SSEF conducts analysis of cobalt-blue spinel from a newly reported source in Tanzania
Quote:
BASEL, SWITZERLAND: MAY 16, 2022
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Figure 1: Cobalt-blue spinel from a newly reported source southeast of Mahenge in Tanzania, together with a vivid pinkish red spinel from a deposit in Epanko, which is close by to Mahenge, Tanzania. Photo: © SSEF


– For several months already a supply of blue cobalt-bearing spinel has been appearing in the gem trade, including some stones of remarkable size –up to 40 carats – and quality. According to information from reliable sources, the source of the new find is a deposit located about 20 kilometres south-east of Mahenge, Tanzania, which for more than 20 years has been known for its red to pinkish red spinel of exceptional quality.

Detailed analyses of a selection of blue spinels from the newly reported source, conducted at the Swiss Gemmological Institute SSEF, has revealed that they contain cobalt as a main colouring element (chromophore), in combination with iron. This is similar to cobalt-spinel materials from sources in Sri Lanka, Pakistan and Vietnam.

Interestingly, reported SSEF, cobalt-blue spinel from the source in Tanzania contains quite characteristic inclusion features, such as oriented geometric lamellae with interference colours (Figure 2), together with lines of fine particles. Similar inclusion features have been described in red Tanzanian spinel from Morogoro. Additionally, colourless apatite and clusters of small zircon inclusions were identified by Raman spectroscopy.
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Figure 2: Oriented lamellae with interference colours together with lines of fine particles are characteristic features of the newly reported cobalt-blue spinels from Tanzania. Photo: M.S. Krzemnicki, SSEF


Gem-quality cobalt-blue spinels are highly sought-after and valued, and consequently have been studied extensively by SSEF. Its laboratory has offered origin determination for cobalt-blue spinel for many years already.

“Cobalt-blue spinel from this new source in Tanzania is a welcome and attractive addition to the trade”, said Dr. Michael Krzemnicki, Director at the Swiss Gemmological Institute SSEF. “It is also fascinating material for us gemmologists to study, as these spinels display specific gemmological characteristics that are helpful for origin determination.”
A more detailed gemmological study of cobalt-blue spinel from this newly reported source in Tanzania will soon be published in a peer-reviewed gemmological journal.

Author:  Stephen Challener [ Fri May 20, 2022 5:45 pm ]
Post subject:  Re: SSEF conducts analysis of cobalt-blue spinel from new so

I saw a post about them on fb, but it was from an unknown source so it's great to see some confirmation! I really want to get some of those lamellae under my scope.

Author:  Barbra Voltaire, FGG [ Fri May 20, 2022 8:37 pm ]
Post subject:  Re: SSEF conducts analysis of cobalt-blue spinel from new so

Stephen Challener wrote:
I really want to get some of those lamellae under my scope.

ditto

Author:  Dioptase [ Thu Dec 15, 2022 3:55 am ]
Post subject:  Re: SSEF conducts analysis of cobalt-blue spinel from new so

The new (well, new-ish now as it has been producing for a bit) cobalt spinel source is an alluvial deposit located near the village of Lukande.

You can find decently sized pieces of rough, and they tend to be relatively clean as far as cobalt spinels go. That's a good plus; I had never seen so many 1 to 3 caraters faceted cobalt spinels before that find.
A lot of what I have seen has often some silk in it, so the crystal appears a bit smoky and muted.


I think the main issue with the Tanzanian material is the color. They have a decent blue overall but the vast majority of them doesn't have the electric blue vividness of the good Luc Yen material. The color is often either too dark, or grayish, or with some greenish undertone.

Some of the Tanzanian material has that punchy color, but these stones are few and far between.

This tiny piece of rough is from the new Tanzanian deposit. Pleasant color, but small.
Image

Author:  Stephen Challener [ Thu Dec 15, 2022 1:49 pm ]
Post subject:  Re: SSEF conducts analysis of cobalt-blue spinel from new so

Thanks for the update! That was about what I expected from the pictures I'd seen but it's nice to hear some of them do approach that true electric blue.

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