Potomac Crystal Ovals - Green Opal (Pacific Opal). Like Rivoli, these crystal ovals have no holes or settings and are designed to be bezeled with wire or seed beads to create gorgeous projects. Use these oval fancy stones to add some extra bling to your designs. The Potomac Crystal Oval will work with any designs calling for a Swarovski 4120 shape. They measure 13x18mm and come in a pack of 2.