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Congratulations to Bobby1 and his Brazilian Agate Cab!

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Author Topic: How to prepare and cut chlorastrolite?  (Read 322 times)

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R.U. Sirius

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How to prepare and cut chlorastrolite?
« on: January 26, 2024, 05:10:33 PM »

I've found this large piece of Michigan "greenstone" - a basaltic matrix with many obvious small nodules of chatoyant chlorastrolite.

I would like to try making small cabochons, but I am not sure how to approach it.

First off, how do I free a nodule from the matrix? Do I chip off with a hammer? Do I grind? Do I leave some of the matrix on the cab, or it doesn't polish at all (feels very gritty) and I should aim for clean nodules only?

Next, exposed nodules seem to be all hollow, with botryoidal turtleback inside surface. Do I make this cavity the back of the cab, and work the convex outside surface? Or should I look for solid nodules to work on?

If you've ever successfully cut this material, please share your insights.


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Re: How to prepare and cut chlorastrolite?
« Reply #1 on: January 28, 2024, 08:01:14 PM »

Greenstone , metamorphosed basalt, can get quite soft. If it hasn't been filled with silica I find it to be about as hard as feldspar .I think you should try leaving your crystal pocket in the matrix and cut the stone gently avoiding extra course diamond. I wonder if oil will harm the pocket content. Careful sanding with nova wheels or the equivalent  should be sfe  and the matrix may only take a matte finish but your pocket contents may polish at 8 or 14 thousand diamond.
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