An unusual natural pearl black onyx and diamond ring. Photo Christie's Image Ltd 2010

The button-shaped natural brownish-grey pearl measuring 14.45mm by 14.60mm by 12.24mm and weighing 18.99 carats (75.96 grains) within a pavé-set diamond surround to the black jade and pavé-set diamond mount, ring size 6½, stamped "750". Estimate $20,000 - $30,000. Price Realized $50,000

Accompanied by report no. 0012374 dated 5 January 2001 from the Gübelin GemLab stating that the pearl is natural

Christie's. JEWELS AND WATCHES: THE DUBAI SALE. 28 April 2010. Jumeirah Emirates Towers Hotel. www.christies.com