Possible Clues:

• In addition are real, cut, gems
• Buck and Bailey
• Lustrous structure in an oyster
• Don't cast these jewels before swine
• Lustrous structures that need no cutting or polishing
• Sound soft, noble and, all told, precious
• Beads from 26dn
• They're found in the shells of oysters
• Accessory for that little black dress
• Lustrous structures inside the shell of an oyster