Shell beads, dyed and over-painted Yellow and Gold, sized 11mm diameter x 2mm thick. Sold as a strand of about 32 beads for your mosaicing pleasure. :) These are quite thin, so you could glue a bead to the back to increase the height, or just stick them onto your finished grouted-then cleaned-up surface. They would add a nice dimension to an abstract mosaic...
Don't be limited by your materials. Play with your tess-array.