Petal pearls are those which are somewhat flat, frequently more pointed at one end than at the other, and have the appearance of a petal or leaf.
Hinge pearls are those pearls that are long, generally pointed at either or both ends, and are found near the hinge part of the shell. They are divided into two distinct forms, namely dog-tooth, and wing-shaped.
Wing pearls: those that are elongated or irregular, resembling a wing or part of a wing.
Dog-tooth: applied to pearls with pointed ears, elongated, and which are narrower than the wing pearls.
Slugs: a name used for the very irregular, distorted pearls, frequently made up of masses or groups of small pearls; usually without luster or form, and of little value except for medicinal purposes.
Nuggets: when the pearls are somewhat round, but are indented or slightly irregular.
Haystacks: when the pearls are either round or oval, with the top considerably elevated.
Turtlebacks: when the pearls are a trifle longer than they are wide, with a domed surface not much elevated. This form is quite prevalent among American pearls.
Strawberry pearls: those that are round or elongated and entirely covered with prickly points, somewhat resembling a strawberry or pickle. It is believed that these irregular marks are frequently produced by minute pearls.
“Blister” and “Chicot” are names applied to those pearls that are found embedded within a nacreous coating, often containing mud, water, or imperfect mother-of-pearl. After these “blisters,” as they are termed, are broken, and layer after layer has been removed from the contents, very fine pearls have frequently been found.