Akoya Pearls

This variety is the most representative of all; the image that comes to mind upon hearing the word "pearl" is most likely that of an Akoya pearl. Nearly all of the pearls cultured in Japan are Akoya pearls, and most necklaces are strung with this variety. The mother oysters are usually palm-sized, so the pearls themselves are not so large, averaging between 2mm and 10mm.
            Black Pearls

Produced from black-lipped oysters in the South Sea (especially Tahiti), these pearls are black, dark green, or dark gray. Also quite popular, and valuable, is the "peacock green" variety, a deep green with a reddish tinge. Other varieties of pearls may be dyed and called "black" pearls, but real, natural black pearls are those taken from black-lipped oysters.
           South Sea Pearls

South Sea pearls are taken from white-lipped oysters, the largest of the pearl oysters. They are a lovely silvery-grey color, and while they can be up to 15mm in diameter, South Sea pearls of this size are very rare and expensive.
           Seed Pearls

When this pearl is brought into existence in the gonad of the mother oyster, it is very small,
resembling a poppy seed. The finished pearl is also quite small, and is produced without a
man-made nucleus. During the cultivation period, the mother oyster takes in some foreign
particle, such as a tiny pebble, and this becomes the core of the pearl. The pearl's shape can be oval, or distorted according to the shape of the foreign matter forming its core.
            Freshwater Pearls

These are cultivated chiefly from the bivalve known as the IKECHOUGAI. Some are raised in Lake Biwa here in Japan, but mostly they are imported from China. Freshwater pearls are generally oval-shaped, and natually-occurring colors include white, of course, as well as orange and wine.
Recently pearl culturing technology has succeeded in producing specimens so large and spherical that many people mistake them for Akoya pearls at first glance.