Hi Rita,
I found this about quarry tile at the freshloaf website
http://www.thefreshloaf.com/node/507
Quarry tiles are genreally considered safe to bake on. The concern is
with glazed tiles which may contain and may release lead in your oven
- not a good thing!
Unglazed quarry tiles are thick and are made of fired clay, basically
as it comes from the ground. Thus it has other things in it besides clay.
Ceramic tiles are generally thinner and but stronger. This is because
they are made from "refined" clay in a powdered form. The end result
is a more uniform tile, thus it is stronger.
Both types are made entirely from earth materials, and if unglazed,
should be fine for baking on. Do not bake on glazed tiles!!!!!
Particularly if from a foreign source. If in doubt contact the manufacturer.
and I found this about fire brick at the fornobravo website
http://www.fornobravo.com/forum/f2/fire-brick-approved-food-contact-6447.html
Firebricks consist of silica and alumina. The clay (silica) part is a
naturally mined substance, and thus may contain other trace elements.
The alumina part is a by-product of aluminum production, and is mostly pure.
I would still like more information if anybody has some.
Dave