Tiny Glassy Dark "Abalone??" Flat-Back Cabochon Ovals 3/8" x 5/16", Pack of 48 #CL-23

So dark, shiny, consistent and perfect, we think they're plastic or glass, machine made, with abalone-like patterning trying to look like abalone.  Intense greens and black, solid black (plastic? foil?) very consistent backs. They're 10mm x 8mm, very small. Domed tops.  Sold per pack of 48.