Faceting Stibiotantalite

Benfield · **Joined:** Wed Sep 28, 2022 4:45 am **Posts:** 1

Hi I wanted to know if there were any tips to faceting Stibiotantalite, I know it is heat sensitive so to be careful with the dop. Thanks Max

glhays · **Posted:** Tue Nov 22, 2022 1:19 am

Looks challenging based on cleavage. Keep us posted on your adventure if you would.

Duncan Miller · **Posted:** Tue Nov 22, 2022 3:13 am

Vargas (1969:307) wrote "Heat sensitivity - moderate [...] This is fairly easy material to handle if proper precautions are taken. The cleavages are not very troublesome. Polishing is fairly easy." They recommend Linde A (AlOx) on tin or tin/lead (use Batt).

glhays · **Posted:** Tue Nov 22, 2022 5:10 pm

Gem Cutting, Sinkankas 1955, 1962 page 282

"Somewhat heat sensitive, dop cautiously. Laps easily and smoothly, polishes well on tin with Linde-A. Differences noted in speed of grinding, direction parallel to the broad face of the crystal being softer than other directions. Crown angles 30° - 40°; pavilion angles 37° - 40°; cut shallow because of dark color and high refractive index."

Sinkankas has a very similar opinion as Vargs on this mineral, I have personally never cut any. I would note that Linde-A has not been around for many years as Union Carbide went out of buisness a long time ago. Probably any good grade aluminum oxide would produce a good result.

jdowney · **Posted:** Fri Nov 25, 2022 6:25 pm

Union Carbide is wholly owned by Dow Chemical since 2001. Still in business however, as is it's former Linde division that was spun off as Praxair in the 1990's. Looking at Praxair's website, Linde A is still produced. Perhaps it is simply not available at the retail level?

https://www.praxairsurfacetechnologies. ... uspensions

Ironically, Praxair and the European version of Linde recombined in 2018 after 101 years of separation - Linde's US holdings were sold to UC during WWI.

I don't think I've ever used Linde A - as you say, any good alumina does just fine in it's place.

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