Interesting. I had to look it up, as I'd never heard of it before. The site I read said in China they make tea out of gold coin grass and it helps to dissolve the stones. I would talk to a vet who is familiar with plants and toxins before I tried it, but it would sure be better than surgery if it wouldn't harm the tortoise (toxic).
I just bought some "kidney tea" from Sensible Health Products. It contains gold coin grass and a couple others, and I have kidney stones. So I'm going to try it to see if it works to help dissolve them.