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 Post subject: Help with polishing of Kyanite
PostPosted: Sun Mar 21, 2021 10:29 am 
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Hello lapidary experts,

what is your experience with polishing on Kyanites? This gem has 2 hardness, 4.5-5 parallel to one axis and 6.5-7 perpendicular to that axis.
So, what exact axis has 4.5-5? It which grow along the crystal or perpendicular to it?

Thanks
Antonis


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 Post subject: Re: Help with polishing of Kyanite
PostPosted: Sun Mar 21, 2021 11:12 am 
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Its been 25+ years since my mineralogy class at university which is the last time I scratch tested a Kyanite, but if memory serves me it is softer along the longer XTL direction.


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 Post subject: Re: Help with polishing of Kyanite
PostPosted: Sun Mar 21, 2021 1:25 pm 
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If you check out the mindat.org site search kyanite, scroll down to the crystallographic section and toggle the Miller indices, the 3d image will give you the exact information on the structure. I have only worked with massive kyanite forms and cabbing, it has properties a lot like most minerals of it's type like selenite, triphane, pietersite. A lot like woodworking, your either on the end grain or not, or somewhere in between. But with my understanding faceting kyanite crystals I would approach it to be like cutting Kunzite, slow, limited vibration, caution on adjoining perpendicular facets edges. Your general question is quite vague, your not even stating what your actually working with "Kyanite's" as you will see on mindat has different forms as do most minerals.

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 Post subject: Re: Help with polishing of Kyanite
PostPosted: Sun Mar 21, 2021 3:32 pm 
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Thanks for your replies.
I'm going to try with my dremel to polish some kyanites of my collection. I'm curious what the result will be.
I checked the planes of kyanite structure on mindat.org and it's more easy to try the plane [001] with my dremel.


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 Post subject: Re: Help with polishing of Kyanite
PostPosted: Sun Mar 21, 2021 6:51 pm 
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Like cabbing the polishing is not all that different than other materials of this type. I would suggest a medium hard felt with Tin Oxide with water, when you get to the actual polish stage. Start with 360/400, then 600/1200, to polish, with cabbing I started with belts 280 to get rough shape, to 400 then 1200 if need fine adjustment I would touch it with a 600 and back to 1200, then to Hard Leather Tin Oxide, if needed touched with Fabulustre polish on a jewelers soft felt buff, carefully not to generate to much heat.

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 Post subject: Re: Help with polishing of Kyanite
PostPosted: Tue Mar 23, 2021 5:02 pm 
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glhays wrote:
Like cabbing the polishing is not all that different than other materials of this type. I would suggest a medium hard felt with Tin Oxide with water, when you get to the actual polish stage. Start with 360/400, then 600/1200, to polish, with cabbing I started with belts 280 to get rough shape, to 400 then 1200 if need fine adjustment I would touch it with a 600 and back to 1200, then to Hard Leather Tin Oxide, if needed touched with Fabulustre polish on a jewelers soft felt buff, carefully not to generate to much heat.

Attachment:
th.jpg


Thank you very much.


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