These are gorgeous cufflinks, and it is interesting that I can't be sure whether they are plastic or glass. When I strike them against glass, they sound like glass, but when I tap them against my teeth, I'm not sure. They are cold on my cheek, but only for a moment. So if you are looking only for glass, you should pass. But if you are only looking for a gorgeous pair of amethyst color cufflinks, these are for you! The "stone" measures 16mm x 12mm, and the overall dimension is 1 1/8" x 3/4".