A pearl is an organic gem and is the only gem that is formed by a small living organism. Furthermore, because a pearl is formed by nature no two pearls are exactly alike, and a pearl that is perfectly round is very rare indeed. A pearl is created by a mollusk (sometimes called an oyster) which is found in the saltwater of an ocean or the freshwater of a lake, river or stream. A pearl is relatively delicate. It is not as durable as gold, glass or a crystal gem. But with a little care, it can last for a very long time, even centuries.
Most people are not aware of how a pearl is formed. It is a fact that most mollusks go through their life span never producing a pearl. Furthermore, when you learn what they go through to survive, you will see that the production of a pearl is truly a miracle of nature. By chance a small little piece of sand or snail gets inside a mollusk and comes out a beautiful pearl. It's pearl magic!
How does this happen? The "foreign body" of some type gets into the mantle tissue flap (a double flap that completely encloses the mollusk) and this irritates the mollusk. To ease this irritation the mantle tissue forms a protective layer of a pearly substance called "nacre" (pronounced "nay-ker") over the irritant. The foreign body makes a depression in the mantle in such a way that a sac eventually develops around the irritant, which then becomes entombed in nacre. Nacre is composed mainly of calcium carbonate in the form of the mineral aragonite (86%), cemented together with a different form of calcium carbonate called conchiolin (12%) and about 2% of water. Spherical pearls are built up in concentric layers-rather like an onion. The size of the pearl depends on the amount of nacre laid over the irritant. Eventually, the pearl itself becomes the foreign body, and starts to be overlaid with more nacre.
It should be mentioned here that only pearls that grow in the mantle or body of the mollusk, however shaped, should be called “pearls”. When a “foreign body”such as a piece of debris sticks to the inside of a shell or a parasite bores through from the outside and gets inside the mollusk’s shell, the mollusk tries to ease the irritation that this causes by forming nacre over the irritant and cementing it to its shell. If this bulge on the shell is a bump or a slight dome, it is called mother-of-pearl. If it is half a sphere or more, it should be called a half-pearl, or a blister pearl. Either way, they can be used as jewels.
