Potomac Crystal Rondelle Beads - Tanzanite. Add some extra sparkle to your projects with these high quality, faceted crystals. With so many colors and sizes to choose from, you’re sure to be inspired and get creative with these beautiful Potomac Crystal Rondelles. Beads measure 3x4mm and come in a pack of 100. *Packages are filled by weight and due to the difficulty of cutting these small crystals uniformly, there may be slight variations in the sizes of the crystals and the number of crystals per package.