I am 99.9% sure it is clay. And I pried up the inlay on one to make sure it is a regular recessed inlay; it is..... ..... .... They are pretty frail; note the small edge nicks. Very unusual chips. As they say, "you will be proud to have one in your collection."

You can have one for $10, postpaid-insured. Set of three for $25 post-paid insured. Non-credit card PayPal accepted.

Robert