Orange Non-nacreous Pearl from a Rare Species, Cassis Cornuta,  Indo-Pacific. Estimate: US$ 6,000 - 8,000 (€5,300 - 7,100). Photo: Bonhams.

The Cassis pearl is an extremely rare natural non-nacreaous pearl, produced by the mollusk Cassis Cornuta and found in the Indo Pacific region. Cassis pearls are found in colors of white, beige brown and orange, the latter being the most prized and sought after pearl. They exhibit a beautiful flame structure that shimmers and dances below its surface. Because of their rarity, Cassis pearls are difficult to acquire with only a small number of these pearls being found each year. 

Of slightly bouton shape, this near-spherical cantaloupe-hued pearl has an excellent porcellaneous surface that features a micro-flame patterned iridescence. 
Weighing approximately 18.55 carats and measuring 13.5 x 13.0mm

Bonhams. LAPIDARY WORKS OF ART, GEMSTONES AND MINERALS INCLUDING GOLD, 19 May 2015 10:00 PDT - LOS ANGELES