FMF - Friends of Minerals Forum, discussion and message board

[Pierre Joubert]

A few years ago, we purchased a number of specimens of Schorl (variety Foitite) from Erongo, Namibia. Most are covered with Feldspar, which has a sand like appearance. Someone I know, removed it by sandblasting, but there is a risk involved with the more delicate specimens. I was thinking about HF acid, but I have always been very weary of using this very dangerous acid. I would welcome any suggestions.

[GneissWare]

Microabrasion is probably the best way. HF will clean feldspar from tourmaline, but if the schorl is fractured and rehealed, it may come apart. Other than these methods, I can't think of anything else that would be as effective.

[Jesse Fisher]

From my experience, schorl is not nearly as resistive to HF as other tourmalines, and can become de-lustered fairly quickly. As Bob suggests, mechanical removal is your best option. Micro air abrasive would be best, but you can also try a water gun. Often, feldspar coatings have been at least partially altered to clay. A quick soak in Iron Out will remove any Fe-oxides and help loosen the clays a bit. Use the water gun or air abrasive before the specimen dries out.

[Pierre Joubert]

Thank you Bob and Jesse. There is not much difference between the hardness of Schorl and Feldspar, but the Feldspar on these specimens is granular, similar to coarse sandstone. I will wait till I get the opportunity to take a lesser specimen to someone who has a sandblaster (with glass beads) and someone who has a high pressure cleaner (I will try the HP cleaner first). I will take photos before and after. Regards