This necklace appears to have two pendants: one round white/black pendant and one oval orange stone pendant.
Here is the closeup:
When I first saw this, I assumed the upper pendant was silver. I believe it’s a white and black pendant. If I am proven wrong I will correct the information.
Beneath the first pendant is an oval, orange stone set in silver. Both pendants are attached to a plastic or rubber chain cord. It could also be a chain of gemstone or quartz stones.
Here it is on Kate: