October 27-28—SACRAMENTO, CALIFORNIA: 82nd Annual Gem, Jewelry, Mineral and Rock Show; Sacramento Mineral Society; Sat. 10-5, Sun. 10-4
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 Post subject: Chrysoberyl cateye
PostPosted: Tue Apr 03, 2018 4:44 am 
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Purchased thie 1 ct chrysoberyl last year in Munichshow.
Orign is Sri Lanka.

Stone has a fine color.

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The cateye is incomplete...

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 Post subject: Re: Chrysoberyl cateye
PostPosted: Tue Apr 03, 2018 5:07 am 
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First pic is in water....

Please forgive the quality - I used my Ipad and it was really difficult to catch the stone through the okular...

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Last one in transmitted light

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The "colorless" areas are free of inclusions - only the brown produce the cateye - hollow tubes, mineral inclusions ??

To my knowledge the inclusions are perpendicular to the c-axis and parallel to the a-axis so the cateye is parallel to the c-axis.

Don't understand why they stopped and than continue to grow...?

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 Post subject: Re: Chrysoberyl cateye
PostPosted: Wed Apr 04, 2018 3:08 am 
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I assume they look brown in transmitted light because of rayleigh scattering from the very fine inclusions. I believe the cat's eye is caused by mineral inclusions rather than growth tubes. I remember someone saying they were sillimanite, though I've found at least one reference to a cat's eye alexandrite with rutile needles: https://www.gia.edu/gems-gemology/winte ... on-pattern, and this 2016 article notes higher levels of titanium in areas with more inclusions, but also suggests that their identity has never actually been firmly nailed down https://www.gia.edu/gems-gemology/sprin ... -australia
As to why they'd be zoned that way, though, it'd be hard to say. Perhaps they represent growth zones during periods with less titanium in whatever it was precipitating from, perhaps it has to do with temperature fluctuations favoring exsolution or reabsorption of needles, or maybe something less straightforward.


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 Post subject: Re: Chrysoberyl cateye
PostPosted: Wed Apr 04, 2018 2:24 pm 
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Thank you Stephen!

Yes - Rutil makes sense..

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