Unlike other jewelry which is made of precious metals and gemstones found deep inside the earth, a pearl is found inside an oyster. Pearls are the result of a biological process — the oyster’s way of protecting itself from foreign substances. Oysters are bivalves, which means that its shell is made of two parts, or valves. The shell’s valves are held together by an elastic ligament. This ligament is positioned where the valves come together, and usually keeps the valves open so the oyster can eat.As the oyster grows in size, the shell also grows. The mantle is an organ that produces the oyster’s shell, using minerals from the food that the oyster eats. The material created by the mantle is called nacre and lines the insside of the shell
The formation of a natural pearl begins when a foreign substance slips into the oyster between the mantle and the shell, which irritates the mantle. The oyster’s natural reaction is to cover up that irritant to protect itself. The mantle covers the irritant with layers of the same nacre substance that is used to create the shell. This is what becomes a pearl.
Not all the pearls are the same. Some are round, some uneven, they come up white, black, gray, red, blue and green.
Cultured pearls are created by the same process as natural pearls, but are given a little help by the pearl harvesters who opens the oyster shell and cuts a small slit in the mantle tissue. In freshwater cultured pearls, cutting the mantle is enough to induce the nacre secretion that produces a pearl.
While cultured and natural pearls are considered to be of equal quality, cultured pearls are less expensive because they aren’t as rare.