Shelled mollusks produce a “pearl” when a microscopic irritant is trapped within its man

Shelled mollusks produce a “pearl” when a microscopic irritant is trapped within its mantle folds. The mollusk creates a pearl sac to seal off the irritation. This is a part of the mollusk’s defense mechanism against a potentially threatening irritant such as a parasite inside the shell, or an attack from outside that injures the mantle tissue. The mollusk’s mantle deposits layers of calcium carbonate in the form of the mineral aragonite or a mixture of aragonite and calcite that are held together by an organic horn-like compound called conchiolin. This combination is called nacre. Natural pearls are nearly 100% nacre (calcium carbonate and conchiolin). This secretion process is repeated many times, eventually producing a pearl. Natural pearls are quite rare. This means that hundreds of pearl oysters or mussels must be gathered and opened just to find even one wild pearl. For this reason pearls were able to fetch extraordinary prices in the past. With the advent of cultured pearls there was a dip in the value of pearls as a reaction to the fact that they were now available to more than just the elite classes. In recent years there has been a steady increase in the value of natural pearls as buyers are drawn to the rarity of natural pearls once again. “Gem” quality natural pearls are still very rare. Values are determined by size, shape, color, quality of surface, orient and luster. *A pair of belle époque natural pearl and diamond pendent earrings, circa 1910 Sold by Bonhams in 2006.* -- source link

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