I have a 10lb steel barbell weight in mine. steel has a lot more mass than ceramic. Lead would be even better. one ceramic tile really would not have much useful thermal mass in this type application. Ceramic is a great insulator...as used on the space shuttle albeit a different compound but still the same principle.
just my 2 cents
I agree that tiles in most forms would not be the most efficient choice. Efficiency being storing the most heat for the space it takes. where as things like water are better and steel as in the weights even better. basically imagine if you left each of those laying out in the sun. which would get hot, hotter and hottest. Tile would get warm to maybe hot, water would probably get a little hotter if it was in a closed bottle, and steel would very likely get to hot to touch. but it is in the end by degrees of effectiveness. And if it is all you have it will work.