"Poor girl seems to be losing her mind. She’s always losing that necklace it seems. Makes me wonder why she takes it off at all." - Concerned Mother in regards to how absent minded her daughter has become
Behold, the luminous isle of the Sapphire Eyed maidens
Topaz you say, looks like a good quality citrine to me. I’ll give you 8 pieces of silver for it.
Galvinus driving a bargain.
Fist sized diamond made famous by the thief Tolky. Stole the ‘rock’ from the Archmage Olikan and made it famous when his hidden thief’s den was found and destroyed by Olikan. The rock was never found though and Olikan searches for it to this day.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.