Black Rhombus Gemstone Bead Strands, Black Stone, Round, Black. about 10mm in diameter, hole: 1mm, about 39pcs/strand, 15.5". Blackstone, with its satiny, moderate gloss polish, is great for accenting or mixing with contrasting gemstones, and blends nicely with either gold or silver beads and findings to be a jewelry which moves office to elegant dining. So buy this 10 strands Black Rhombus Gemstone Beads For $7.69 @PandaHall.