Ayvee of Diana’s Jewels very astutely points out that the stones on this yellow gold ring correlate with Kate’s and William’s birth months.
Many people speculate that it was given to Kate as a gift from William because she started wearing it while she was dating him.
The ring is a somewhat thick band studded with pearls and garnets (June’s gemstone is pearl, January’s is garnet). It doesn’t look like the gemstones surround the entire band. They appear to cover the visible part of the ring only.
She wore it while visiting Action on Addiction in 2013.
It also looks like she is wearing it in this photo from March 2012 when she visited the UK Scouts at the Great Tower Scout Camp.