Trustmark 925 Sterling Silver 1.3ct 6mm Black Created Opal Cabochon Crown Set Stud Earrings, Aurora Features our popular 6mm cabochon size which measures about 1/4 of an inch. Made with created Black Created Opals! Professionally hand-set in our own US studios. Style or Setting: Solid 925 Sterling Silverheavy-duty 4 point Hold Tight Crown Setting.