Kate frequently wears these classic pearl earrings, updating them for her modern look with a diamond studded gold hoop to dangle them from.
The pearls themselves are rounded with a slight egg shape. The connector hoop is made of 18ct yellow gold. They are officially called Classic Baroque Pearl Earring Drops
It is believed that the diamond hoop she uses when she wears these is made by Kiki McDonough. This appears to be the case, since photo comparisons between the Classic Green Amethyst and Diamond earrings show that the hoops are of a similar size and appearance, and they also allow for some space between the hoop and the earlobe.
Kate has worn these numerous times. The most recent appearance of these pearl drops was when she visited the Downton Abbey set at Ealing Studios.
Some other appearances:
World War I Centenary in Belgium (2014):
Trooping the Colour in 2014.
The retail value of these drops is £295 or approximately $467.