Awful little things, far too small to cool your drink, and they arrive very dirty and really sharp. Scratched my lovely new glasses on the first use despite us being extra careful and having washed them thoroughly. Also the tiny, cheap bag they came in smelled like rotten milk and looked nasty. Went straight into the bin.
Can only imagine the soapstone ones are better but shan't be trying rocks again, regardless.
Sad times. Don't waste your money.