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 Post subject: Rainbow lattice .... garnet?
PostPosted: Wed Aug 23, 2017 1:30 am 
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I was just cutting this Mali garnet and noticed some silk. With a bit of magnification, it looks like the famous rainbow lattice sunstone from Australia. Is this common in garnet? (only my second cut in this material) Is it caused by the same inclusions (rutile and hematite I think)?

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In other news .. my gem turned out horribly cloudy :cry:


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 Post subject: Re: Rainbow lattice .... garnet?
PostPosted: Wed Aug 23, 2017 2:56 am 
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That's really strange. :shock:
I know there is a locality for iridescent andradite in Japan, but it seems to be closer to labradorite in presentation at best and is apparently limited to a thin layer.

The closest thing I can find to your mali is these garnets from mexico and this cabochon on thegemtrader. Both suggest a different cause to the usual japanese iridescence.
That beats the usual jardin though! First time I've heard of rutile silk in a non-red garnet on here.


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 Post subject: Re: Rainbow lattice .... garnet?
PostPosted: Wed Aug 23, 2017 12:27 pm 
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So-called Mali garnets are a mixture principally of the andradite and grossular species. It's the andradite content that gives some of them their special brilliance. Since iridescence is known in some andradites it seems possible to me that such inclusions could be found in Mali stones. However most descriptions of Mali garnet properties mention that sometimes small mineral crystals are found along parallel growth planes. Your observation is interesting.

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 Post subject: Re: Rainbow lattice .... garnet?
PostPosted: Wed Aug 23, 2017 12:41 pm 
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Interesting. Thanks for posting this gemological curiousity.

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 Post subject: Re: Rainbow lattice .... garnet?
PostPosted: Wed Aug 23, 2017 5:42 pm 
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Irridescent rutile is fairly common in garnets, though it is rarely that coarse. I would guess that's what you're seeing though. I don't know any reason that it couldn't be hematite/ilmenite as in rainbow lattice sunstone, but I don't think of hematite as a particularly common inclusion in garnet, maybe because iron would be perfectly happy to mix into the garnet itself.


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 Post subject: Re: Rainbow lattice .... garnet?
PostPosted: Wed Aug 23, 2017 6:27 pm 
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Thanks to everyone for sharing your knowledge, fascinating stuff!


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