The Regent Diamond

Louis XV used this 140,6 carats (!) for his crown created in 1722 but it was Philippe, Duc d'Orlèans who initially bought it from Thomas Pitt in 1717 allegedly for 650.000 American dollars. Since Philippe was regent at the time for the future Louis XV the diamond was simply named "the Regent Diamond". Such a diamond must be shared and Marie Leszczynska wore it in her hair. Later on Louis XVI also had it laid into his crown before he gave it to Marie Antoinette as a present. She is said to have worn it in a large black velvet hat.

The Regent

It is cut in a cushion shape and is mostly white but has a slight blue shine to it. The diamond is 47,6 mm tall, 31,75 mm wide and 34,92 long. It was found in the Parteal mine in India.
The Regent Diamond was among those stolen from the collection of French royal jewels in 1792 - but at that time neither Louis XVI nor Marie Antoinette would have had any occasion to use it... Napoleon managed to accumulate the diamond and wore it on his wrist for a short period. Today it is exhibited at the Louvre.

Replica of Louis XV's crown - the Regent would have been
the main body of the fleur-de-lys