Kate was visiting a nightclub in 2007 when she wore these statement earrings.
Here is the closeup:
They are extremely large earrings. A burnished ball post is the anchor for the pear shaped pendant. The pendant is a concave silver disc with a rim of silver at the borders. It looks like the pendant is gunmetal gray while the ball post is a yellowish gray.
I estimated that these are perhaps 3.5 inches long, maybe even longer.
Here is a clearer photo of her wearing them.