Find a local pottery supply place, and get a cordierite kiln shelf. Same thing... much cheaper!
I'm serious...jus paid half their price on a 21 in. round 3/4 " ......seen it as high as $72 though so let the buyer beware...
This chit is tough man, can't you tell.........Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18). A high temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.