I was wondering about lava blocks recently on another post when I saw a Kabob with a bit of lava stone on it. I had read in various places that lava wasn't good for hamsters, but as Cypher pointed out, I already had a lava ledge and that didn't seem to cause any problems. Plus hamsters usually aren't that interested in eating lava I think. Personally I don't think it would be a good idea for a hamster to chew/eat lava - and there are plenty of other chews that are good for them. The antos chews are very popular although not sure if you can get them in the US.
Something like this might be better, and you can slide the wood chews up and hide treats between the blocks. I think wood is better for chewing.
http://www.amazon.com/Kaytee-Perfect...=hamster+chews