Credit goes to My Small Obsessions for the ID.
To Trooping of the Colour 2016, Kate wore these huge mabe pearl earrings.
They are the Balenciage Faux Pearl and Crystal Ear Cuffs.
The earrings are clip-ons. I think this may be a first for Kate. She has only publicly worn hook or post earrings to my knowledge.
They are set in silver toned metal and surrounded by white crystals.
Here they are on Kate:
She pulled them out again when she attended an event to commemorate the 100th anniversary of the Battle of Somme.
These cost $745 USD.