Abalone pearls are very unusual. They are identified by their hollow structure and highly iridescent nacre.
Baroque pearls are neither round nor symmetrical, but very distorted and irregular in shape.
Black-lip oyster is responsible for producing black pearls which are very rare.
Blister pearls are naturally caused by the intrusion of a parasite into an oyster. The mollusc secretes nacre over the irritant, cementing it to the shell itself.
Colour of pearls is influenced by the type of pearl oyster; an important factor in pearl selection.
Cultured pearls are formed by the insertion of a piece of mantle tissue into the mother oyster or mussel.
Freshwater pearls are flesh-nucleated pearls from freshwater shellfish.
Gold-lip oyster's inner shell edge is often golden yellow, and it usually produces yellowish or golden-coloured pearls.
Grain is a unit of measure for natural pearls; one grain equals 0.05 grams or 1/4 carat.
Lustre is the appearance of a pearl's surface, judged by its brillance and ability to reflect light. Also called "sheen" or "shimmer". See Orient.
Mabe pearls are formed when a half-bead is cemented to the mollusc's inner shell. It is covered with nacre and when the shell is cut off, the bead is exposed at the back. The bead is removed, the pearl cleaned and the remaining hole filled with paste or wax. Then it is covered with a mother-of-pearl backing.
Mantle is the part of an oyster's anatomy that secrets nacre.
Momme is an ancient Japanese unit of weight, still used for cultured pearls. One momme equals 3.75 grams.
Mother-of-pearl is the smooth, hard pearly lining on the interior shells of certain oysters and other molluscs, used to make beads, buttons, cameos and other decorative objects.
Nacre (NAY-ker) is the pearly substance secreted by the mantle of certain molluscs to form a pearl.
Natural pearls are formed entirely by accident and without the intervention of man.
Non-nucleated pearls are formed by the insertion of tissue only.
Necleus is inserted into a pearl-producing oyster to speed up the pearl growing process. The nuclei act as the irritant.
Off-round pearls are slightly flattened or ovalish in shape.
Orient is the typical pearly lustre seen on pearls or mother-of-pearl shell. Also known as iridescence.
Osmena Pearls are not pearls at all, but the inner layer of shell from a chambered nautilus. This inner shell is usually white with a rainbow of iridescence and are normally slightly ridged.
Round pearls are perfectly round in shape.
Semi-baroque pearls are not round in shape; examples are pear, drop, egg, and button shapes.
Shape is one of the most important criteria in pearl selection. Pearls can be divided into four basic shape categories: round, off-round, semi-baroque and baroque.
Silver-lip oysters produce silvery white pearls.
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