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 Post subject: Pink axinite from Merelani, Tanzania:
PostPosted: Sun Sep 06, 2020 2:19 pm 
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I have been reading an article in Gem-A's The Journal of Gemmology on Pink Axinite from the Meralani District of Tanzania.

What a wondrously beautiful and rare discovery.
Quote:
ABSTRACT
Associated with an intense geological event from-820 to-520 My, East Africa was the place of major metamorphism. It yielded several mineral resources including high-quality gemstones. Those treasures are markers of the geological conditions during their formation. A relatively common mineral-axinite-is found in Merelani (Tanzania) with a rare undocumented pink colour of mysterious origin with an uncommon orange luminescence. We have characterized two extremely rare "pink" axinites from the famous Merelani deposit with classical gemological methods, energy-dispersive analysis on a scanning electron microscope, UV-Visible, Raman and luminescence spectroscopies. We compared the two pink samples to three other crystals from Merelani and one axinite-(Fe) from Oisans (France). Chemical analysis revealed the two pink axinites corresponded to axinite-(Mg). The pink to purple colour is due to a large broad band centred around 550-560 nm. Its position and shape are typical for Mn 3+. Manganese is present in both pink samples as Mn 2+ , and we surmise that radiation from nearby minerals or rocks converted some Mn 2+ into Mn 3+. The orange luminescence-weaker under shortwave ultraviolet-of the six axinites is related to a broad emission band at 631 nm caused by Mn 2+ and the more unusual red luminescence is associated with two sharp peaks at 688 and 694 nm attributed to Cr 3+. This unique mineralization expands our knowledge of the impact of local lithology on gemstone colour.

Image
Axinite from Tanzania: 15.5 x 8.9 x 13.5 cm. (Photo: Mia Dixon), Courtesy of Pala Gems

Standard Gemological Characteristics

Very strong pleochroism
Tanzanian (Mg) axinite is biaxial positive, whereas other axinite is biaxial negative.
Crystal Structure: Triclinic, platy crystals
Hardness: 6.5 - 7 on the Mohs scale
Refractive Index: 1.656 - 1.704
Density: 3.26 - 3.36
Cleavage: Good
Transparency: Transparent, translucent
Double Refraction / Birefringence: -0.010 to -0.012
Luster: Strong, vitreous
Fluorescence: Red orange LWUV



Do any of you have this material?


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 Post subject: Re: Pink axinite from Merelani, Tanzania:
PostPosted: Sun Sep 06, 2020 2:29 pm 
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Yes, crystals of pink axinite are pretty commonly available at Tucson. Many also show a color change to blue/purple. I picked up a nice little parcel this year.
Axinite is just one large deposit of gem-grade material away from being the next tanzanite. Its range of colors includes sapphire blue and emerald green (though only generally seen as little splotchy zones in some crystals) as well as this pink and tanzanite-like blue-purple, plus the more common topaz-like colors. If you get the right axinite with blue splotches it can have a rainbow look as it is turned because of strong zoning and strong pleochroism within each zone. It even already has a marketable name!

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 Post subject: Re: Pink axinite from Merelani, Tanzania:
PostPosted: Sun Sep 06, 2020 3:06 pm 
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Oh, be still my heart.
What is the average size of the cut gems?

And, please everyone pray that the Home Shopping Channels don't pick this one up.


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 Post subject: Re: Pink axinite from Merelani, Tanzania:
PostPosted: Sun Sep 06, 2020 4:05 pm 
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Cut stones of the pink or blue/purple material are fairly rare, I haven't priced any of those out. The crystals are flat (even more so than your typical wedge-shaped axinite) and usually included. I'd be happy to send you one of the color change/shift crystals once I dig them up.

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 Post subject: Re: Pink axinite from Merelani, Tanzania:
PostPosted: Sun Sep 06, 2020 5:08 pm 
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I'll definitely take you up on that. I'll holding my breath but I'm no Houdini.
GASP, holding my breath is over.


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