This brooch features three thistles with diamonds and gold and silver, possibly a white metal, for the leaves.
The Press Association, according to From Her Majesty’s Jewel Vault, reported the brooch was a gift from the Sultan of Oman, part of a set of four given to Her Majesty. It is likely, as FHMJV posits, that the other three depict representations of the other nations of the UK, with this brooch using the flower of Scotland. It first appeared in 2012, likely making it a Jubilee gift.