Non-nacreous Scallop Pearl, Pectinidae sp.,  Sea of Cortez, near Baja California Peninsula, Mexico. Estimate: US$ 2,500 - 3,500 (€2,200 - 3,100). Photo: Bonhams.

A scallop pearl is a non-nacreous calcareous concretion produced by any member of the pectinidae (scallop) family. Unlike other non-nacreous pearls, such as the melo-melo and conch pearl, the scallop pearl comes from a bivalve mollusk. Scallop pearls are native to the coastal waters of Central and North America and most commonly found off the coast of Baja California Peninsula. The scallop pearl is a very rare occurrence and is the bi-product of wild-harvested scallops. A typical scallop fisherman might discover a mere handful throughout his entire career.

Due to the rarity of the gem, scallops are not sought for their pearls. Scallop pearls have a unique shape and coloration absent in other calcareous concretions. They are generally symmetrical in an oval, round, drop, or button shape. 

Displaying a perfect drop-shape, the present offering is a highly symmetrical pearl of virgin white color, with excellent luster. 
Weighing approximately 17.10 carats and measuring 16.5 x 12.0 mm

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