A 19th century pearl and gem-set brooch/pendant. Photo Bonhams

The highly stylised foliate plaque, with a central cushion-shaped amethyst, within a ropetwist border and rose-cut diamond surround, suspending three natural pearl drops, surmounted by a similarly set cushion-shaped topaz in a foiled closed back-setting, highlighted by further rose-cut diamonds throughout, mounted in silver and gold, later brooch fitting, length 6.0cm. Estimate: £12,000 - 18,000, US$ 19,000 - 29,000

Accompanied by a certificate from The Gem & Pearl Laboratory stating that the pearls were found to be natural, saltwater. Certificate number 05192, dated 7th February 2012.

Bonhams. Fine Jewellery, 25 Apr 2012. London, New Bond Street www.bonhams.com