Pearls are the only gemstones made by living creatures. Mollusks produce
pearls by depositing layers of calcium carbonate around microscopic
irritants that get lodged in their shells, usually not a grain of sand as commonly believed.
While any shelled mollusk can technically make a pearl, only two groups
of bivalve mollusks (or clams) use mother-of-pearl to create the
iridescent “nacreous” pearls that are valued in jewelry. These rare
gemstones don’t require any polishing to reveal their natural luster.
Appropriately, the name “pearl” comes from the Old French
perle, from the Latin perna meaning “leg,” referencing the
leg-of-mutton shape of an open mollusk shell. Because perfectly round,
smooth natural pearls are so uncommon, the word “pearl” can refer to
anything rare and valuable.
The rarest and most expensive pearls are natural pearls made
in the wild, without human interference. The majority of pearls sold today are cultured or farmed by
implanting a grafted piece of shell (and sometimes a round bead) into
pearl oysters or freshwater pearl mussels.
Pearls are very soft, ranging between 2.5 and 4.5 on the Mohs scale.
They are sensitive to extreme heat and acidity; in fact, calcium
carbonate is so susceptible to acid that authentic pearls will dissolve in
The finest pearls have a naturally reflective luster, making them appear creamy
white with an iridescent sheen that casts many colorful hues.
Cultured freshwater pearls can also be dyed yellow, green, blue, brown,
pink, purple or black.
Black pearls, which are mostly cultured because they are so rare in
nature—aren’t actually black but rather green, purple, blue or silver.
Pearls used to be found in many parts of the world, but natural pearling
is now confined to the Persian Gulf waters near Bahrain. Australia owns
one of the world’s last remaining pearl diving fleets and still
harvests natural pearls from the Indian Ocean.
Today, most freshwater cultured pearls come from China. South Sea pearls
are cultured along the northwestern coastline of Australia, the
Philippines, and Indonesia.