Originally when I started rock tumbling I took a bunch of stones from my backyard and tossed them in the barrels to see what would/wouldn't tumble.
I liquified about 75% of the rocks I tossed in (too soft/sedimentary), and a lot of them wouldn't hold a polish.
I recently went back and ran these 'surviving' stones through my UV-18 vibe tumbler...much better now! (shown below)
Photo #275
https://ball-pythons.net/forums/cach...ked_d7vvty.jpg
66% Het Clown shown above