Hi Everybody!

One of the most frequently asked questions that we hear at PurePearls.com is “What really determines a pearl’s size?”  There are quite a few reasons that we can delve into here, but the first (and biggest) reason is the size of the oyster itself!  For simplicity, we’ll deal with the cultured saltwater pearl oysters here and leave cultured Freshwater pearls for another day. The Akoya pearl producing oyster is the smallest of all saltwater producing mollusks, while the Tahitian and South Seas pearl oysters are the larger pearl producing types known today.   

The Akoya oyster Pinctada martensii reaches maturity at about 3 years old and grows to about 7cm long; not very large!  Due to its smaller size, this saltwater oyster can only accept one or two small bead nuclei implanted in the gonad (the animal’s reproductive organ) during the nucleation procedure, and produces smaller pearls in the 2.0-9.5mm size ranges, with pearls over 8.0mm considered very large and rare.  The colder northern waters that host P. martensii cause the animal to deposit nacre at a slower rate compared to their more exotic cousins creating thinner, more transparent aragonite platelets and a higher luster.  A reduced pearl growth timeline of 18 months also ensures that these pearls remain in the smaller size ranges.  

Black Tahitian pearls are produced by the black-lipped Pinctada margaritifera oyster (the Latin translation of margaritifera means “My Lovely”), which at maturity can reach up to a foot in length.  This means that the bead-nuclei used during the pearl culturing process can be much larger than that of the Akoya oyster, with many pearls ranging in size from 8.0-16.0mm with the occasional pearl reaching close to 20mm in size!  Commonly found in the warmer waters of French Polynesia, the pearls are nurtured carefully throughout their 2 year growth period to ensure the standard minimum of 0.8mm of nacre is deposited around the bead.  However, an average nacre thickness of 1.5-2.5mm is most commonly found and lends the pearls a satiny luster that is very pleasing. 

Lustrous Golden and White South Sea pearls from Australia and the Philippines round out the list.  These gorgeous pearls come from the oyster Pinctada maxima, of which there are two types: Silver-lipped and Gold-lipped.  Both oyster types can grow up to a foot in diameter.  As the largest oyster variety in the ocean, it can also accept larger shell bead nuclei.  Pearls will range in size from 9.0-20.1mm, with an average pearl size of 13.0-14.0mm!  The warm, clean waters of Australia and the Philippines allow P. maxima to deposit their nacre layers very quickly (the warmer temperatures speed up the oyster’s metabolism). Their 2 year growth period ensures a thick layering of nacre averaging between 2.0-4.0mm!  These thicker nacre layers are what endow the South Sea pearls their trademark soft, satiny glow that is renowned the world over.