During her early 20s, Kate was spotted wearing this white necklace.
The above photo was taken in April 2007.
Here is a close up.
Update: My Small Obsessions has a better closeup, which I will post here.
The necklace appears to be made of white discs (possibly made of plastic, but I’m not sure). The discs overlap each other and are attached to a slim
white cord strand of white beads that wrap around the neck.
Here is another photo of her wearing this necklace. This might have been taken in 2006 or 2007.
My best guess is that this is costume jewelry. I can’t think of a particular company that makes this necklace, but in my search I did find one of a similar style in case anyone is interested in this type of necklace. Here it is.