An 16.25 carats Colombian emerald and diamond ring. Estimate £100,000 - 150,000 (€140,000 - 210,000). Photo: Bonhams.

The rectangular step-cut emerald, weighing 16.25 carats, between geometric stepped shoulders set with baguette and square-cut diamonds, diamonds approximately 1.50 carats total, maker's mark, French assay mark, ring size Q, cased by Garrard & Co, 24 Albemarle St, W.

Accompanied by a report from Gübelin, stating that the emerald is of Colombian origin, with indications of minor clarity enhancement. Report number 13100238, dated 22 October 2013.

BONHAM'S. FINE JEWELLERY, 22 Apr 2015 14:00 BST -LONDON, NEW BOND STREET