IF/854 Vintage buying small moss agate silver brooch by John Hart, Iona, hallmarked 1964

A small vintage silver set cabochon moss agate brooch by John Hart, marked "IONA" and hallmarked in Edinburgh in 1964 though it may buying be 1960 as the date letter is small and a bit rubbed. It's 2.5 cm or an inch up and across has a good pin and safety "C" catch, the moss agate cabochon has green strands and a red rust patch and a clear semi transparent area and the silver visible to the front has a braided or knot pattern.
The John Hart mark has been lightly struck and right at the position that you would hold the brooch as you pin it on so it's badly worn, you can just make out the vague shape of the shield and the conjoined JH.