Potomac Crystal Bicone Beads 4mm - Tanzanite. The exclusive PotomacBeads Crystal Bicone is a machine cut bead with faceted edges to give you that extra pop of sparkle to your bead weaving designs. They come in a broad range of colors and sizes so you’re sure to find the perfect fit for your next project. Use these brilliant crystals for any designs that formerly called for Swarovski 5128 or Preciosa 4mm bicone. Appoximately 120 beads per package. 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.