The most prized pearls are taken from saltwater molluscs and are classed as Oriental. The larger the pearls are the more valuable they are.
Larger pearls are very common.
A smaller pearl that has a rounder shape can be more valuable than a much larger irregularly shaped pearl. I rregular shaped pearls are called Baroque and are less in value. The shade of the pearl also adds to its value. Black pearls are very rare and value could also depend on the structure of the pearl and the way it was formed. The most valuable colors are white, cream rose and black.