I've just made something with this gorgeous rainbow mystic topaz I bought, but I am afraid of tumbling it. Has anyone tumbled something with one before? I'm afraid it might scratch! It's a faceted oval with a concave back.

Thanks

 Good call. Just to be on the safe side I wouldn't tumble it.

Mystic topaz is a regular topaz specially coated in a fine layer of titanium oxide particles. Remove the particles and you'll lose that pretty iridescence.   

I'd stick with a polishing cloth for the metal on that piece.

~Addie~