The Williamson brooch was made in 1953 by Cartier for Queen Elizabeth II.
It's named after Dr Williamson, a Canadian geologist who owned a diamond mine in Tanzania. In 1947, his mine unearthed a flawless pink diamond, which he presented to the then Princess Elizabeth as a wedding gift (she got married in 1947).
Cartier then cut the stone and set it in a jonquil-flower brooch with 200 white diamonds.
The original uncut pink diamond weighed 54.5 carats. The pink cut diamond at the heart of the brooch weighs 23.6 carats.
The Queen wears the brooch frequently. Most notably she wore it in 1981 to the wedding of Prince Charles to Lady Diana Spencer.
