Red obsidian stone, semi precious stone, oval, flat back, focal stone, smooth domed stone, opaque, stone. Measuring 18 x 13mm. Will fit in many of our 18 x 13mm mounts. The color is very unique, dark coffee brown color with black. We cull our stones for quality to make sure of no cracks or chips and that the over-all appearance of the stone is very pleasing. You should expect variations in all natural, semi precious stones. No two stones are exactly alike. Sold by the piece.