The Carrs/C&L ballast was crushed nut cases, I say was because I don’t know the present situation as I believe the factory that made it went up in smoke with disastrous consequences not too far from here, including loss of life. Court cases have been ongoing for some time though I think they may have now been concluded. This was a few years ago, so presumably a fresh source has been found.
Chinchilla dust can be good but it can be difficult to get the right size. In any event it’s a lot cheaper. I always thought that Woodland Scenics ballast was stone based.