OK, I'll try to remain calm when talking about "clay" chips on eBay.
THE CHIPS AIN'T CLAY! THE SELLER IS LYING!!
Clay sells so everyone claims they have clay chips. They put "clay" in the description so they get included when people search for that. And since everyone else claims they have clay chips, all the sellers have to say this just to keep up with the competition.
But no way... no way in hell. These are plastic chips from China, period. They have a metal slug in the middle (use a magnet and see for yourself) to make them 11.5 grams.
Your question is not dumb, we all went through it.
Please use one of the best resources around, the review sites. Start here
http://www.pokerchipreviews.com/education.html then go to the home page and continue to read all of that site, plus
http://www.homepokertourney.com/chips.htm and the rest of that site.