These are 2 unusual beach finds found on different visits at the same Tampa Bay beach, Florida. Approx. sizes 1 1/2-1 3/4 x 3/8 inch and about 1/16 inch thick. They look like brown wood grain with fine grooves on one side and shiny enamel-like on the flip side. They are slightly curved. Initially I thought it was a stingray barb but it has no barbs. Than I thought a seashell fragment but it doesn't resemble any seashell I'm familiar with. So what are they?