The term “fresh-water” is given to those pearls that are found in the fresh-water brooks, rivulets, rivers, or fresh-water lakes, and not in salt water, and which belong to the Unionidæ.
The term “conch” is applied to that variety of pearl which is usually pink, or yellow, in color, and that is either found in the univalve shell, known as the common conch (Strombus gigas), or in the yellow shell (Cassis madagascarensis).
The word “clam pearl” is used to designate those pearls that are found in the common clam of the Atlantic coast, and are either black, dark purple, purple, or mixed with white, more especially if they are boiled.
“Placuna pearl” designates those pearls that are found in the Placuna, or window-glass shell, in the East. They have a micaceous luster, are rarely of much value, and are sold entirely in the Orient, almost exclusively for medicinal purposes.
“Oyster pearl” signifies those concretions that are found in the common edible oyster (Ostrea). They are generally black, purple, or with a mixture of black and white, or purple and white. They are devoid of nacreous luster and possess neither beauty nor value.
“Coque de perle” designates the globuse walls of the nautilus and possibly other shells that have a pearly nacre; they are almost hemispherical and are either round or long, having a pearly effect.
“Abalone”: a name applied to those pearls that are found in the univalve “ear-shell” or awabi, as it is called in Japan. They are generally green, blue-green, or fawn-yellow, and have an intense red, flame-like iridescence. They are rarely round, generally flat, or irregular, and are occasionally worth several hundreds of dollars each.
“Pinna pearls”: those pearls that are found in the Pinna, or wing-shells of the Mediterranean and adjacent seas. These possess no orient, but are more highly crystalline than any other pearls. They are almost translucent and have a peculiar red or yellow color, and are of little value except locally.
“Cocoanut pearl”: this name is given to those pearls that are found in the giant oyster or clam of the vicinity of Singapore; they are erroneously called cocoanut pearls because they have the appearance of the meat of the cocoanut. They are often of great size, but have no commercial value.
The following are special designations of the different varieties of pearls according to their forms and appearance: