Kate wore these just once to the BOA Olympic Concert on May 11, 2012.
Here is the closeup:
These are elongated, teardrop-shaped pave encrusted earrings. The front of the earrings is covered in pave stones. The back is not.
The editor at Diana’s Jewels believes that these are costume jewelry pieces, and I agree.
The appearance of the back, the ear stopper and the closed post setting all indicate that this is not fine jewelry she is wearing.
I don’t know where Kate got her pair, but I found a similar looking pair from Debenham’s.
They’re made by Julien MacDonald and their official name is Gold Pave Crystal Teardrop Earrings. On Polyvore, they’re $25.