Pearl Quality Factors
Pearls are hard, rounded objects - the natural formation of a secretion called nacre that is produced by certain mollusks, primarily oysters. The process begins when an irritant such as a grain of sand or a piece of tiny shell, gets inside an oyster's shell. In order to protect its delicate body flesh, the pearl oyster secretes nacre to surround the irritant and never stops, so over the years the nacre layers build up into a pearl. In short, the pearl is, like the shell, a product of bio-mineralization and crystallizes from a living organism.
Usually, it takes more than 2 years for oysters to cover the irritant with layer upon layer of nacre i.e. to form a pearl. A quality pearl requires certain thickness of nacre. Pearls are valued as gemstones and are cultivated or harvested for jewelry.