Pinna Pearls from the Wing-Shell

Pinna pearls...the structure of these pearls differs from most natural pearls.

Pinna pearls...a few pearls are obtained from the sea-wings or wing-shells (Pinna), the silkworms of the sea, found in the Red Sea, the Mediterranean Sea, the Indian Ocean, the southern coast of America, and elsewhere.

These shells are narrow at the unbo, or hinge, long, and fan-shaped; they are generally brittle, and present a horn-like appearance. The interior is commonly of a silvery reddish or orange-colored hue, and this tint is imparted to the pearls.

The most characteristic feature of Pinna is the thick rope of silky fibers, from four to ten, and sometimes twenty or more inches in length, constituting the byssus, a remarkable provision by means of which it anchors itself to the bottom and thus outrides the storms.

Formerly the byssus was gathered in Sicily, washed in soap and water, dried, corded, and fabricated into gloves and similar articles of a fine texture. The finished garments were of a beautiful golden brown color, resembling the burnished gold on the backs of some splendid flies or beetles.

The yield of Pinna pearls is very small. A few are obtained from the Mediterranean, especially on the Adriatic coast. These are usually rose-tinted or reddish in color, but of diminished orient, and inferior in size. Pinna pearls are also reported from the Isle of Pines and from New Caledonia, where they are commonly very dark, almost black in color.

Pinna pearls possess no orient, but are more highly crystalline than any other pearls. They are almost translucent and have a peculiar red or yellow color. Pearls produced by the Pinna squamosa are generally brown in color.The structure of pearls from some bivalves,as the Pinna, for instance, differs from that of the true pearls formed in species of Margaritifera. Instead of the alternate layers of conchiolin and of carbonate of lime, many of these have an alveolar structure. When greatly magnified, the surface of Pinna pearls appears to be formed of very small polygones, which, as decalcification shows, are the baes of small pyramids radiating from the nucleus. The walls of these pyramids are formed of conchiolin, and they are filled with carbonate of lime of a prismatic crystalline structure.

Information by Kunz and Stevenson in 1908.

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