Some of the best pizza stones are made from Cordierite. Some can be expensive.
However you can pick up the exact same stones at a pottery store that has supplies for Kilns. I purchased a 15x16" 5/8" thick for $17+ tax. This stone is good up to 2100 deg F. The difference the kiln stone and pizza stone version, the kiln doesn't have a FDA safety sticker.
I use it in the weber kettle or my elect. oven. In the weber kettle I can get temps up to 700-800 deg. for short periods, and cook a pizza in 2 to 3 minutes.
When I purchase the Cordierite stone, the guy helping me, told me he sells them to various pizza and other restaurants as replacement stones in their ovens.
Search my name and you will find several posts on making pizza in a weber kettle.