I recently bought a record player, and have been frequenting local D.I.'s (a kind of thrift store, but not yucky smelling like the salvation army) and purchasing random records. So far they all seem to be made of plasticish material thats light and flimsy, except one. It was in the wrong case, and its made of something really hard and dark. It feels like glass to me. I can't see any scratches, but the sound is really bad quality.
Any idea what its made of, and what time period it would have been produced?