The Exquisite Sapphire is a unique miscellaneous item added by The Elder Scrolls V: Dragonborn. It appears to be of a lighter blue and to be quite shinier than a regular sapphire.
Background
Sapphire tells the Dragonborn that she always carried around this sapphire for good luck.
Acquisition
Obtained by bringing Glover's Letter to Sapphire.
Glover's Letter respawns, allowing the letter to be given repeatedly and the sapphire infinitely acquired.
Usefulness
It is the single most expensive miscellaneous item in The Elder Scrolls V: Skyrim, and has the highest value to weight ratio in the game, not counting items with zero weight such as gold.