Pearlsofnature - definition of a pearl

Pearls from other species:

Different types of cultured pearls, including black pearls, frequently referred to as Black Tahitian Pearls, are highly valued because of their rarity; the culturing process for them dictates a smaller volume output and can never be mass-produced. This is due to bad health and/or non-survival of the process, rejection of the nucleus and their sensitivity to changing climatic and ocean conditions. Before the days of cultured pearls, black pearls were rare and highly valued for the simple reason that white pearl oysters rarely produced naturally black pearls, and black pearl oysters rarely produced any natural pearls at all.

Since the development of pearl culture technology, the black pearl oyster found in Tahiti and many other Pacific Island areas has been extensively used for producing cultured pearls. The rarity of the black cultured pearl is now a “comparative” issue. The black cultured pearl is rare when compared to Chinese freshwater cultured pearls and Japanese or Chinese Akoya cultured pearls and is more valuable than these pearls. However, it is more abundant than the South Sea pearl, which is more valuable than the black cultured pearl. This is simply because the black pearl oyster Pinctada margaritifera is far more abundant than the elusive, rare, and larger south sea pearl oyster Pinctada maxima, which cannot be found in lagoons, but which must be dived for in a rare number of deep ocean habitats or grown in hatcheries.

Black cultured pearls from the black pearl oyster – Pinctada margaritifera – are not South Sea pearls, although they are often mistakenly described as black South Sea pearls. In the absence of an official definition for the pearl from the black oyster, these pearls are usually referred to as “black Tahitian pearls”.

The correct definition of a South Sea pearl is a pearl produced by the Pinctada maxima pearl oyster. South Sea pearls are the colour of their host Pinctada maxima oyster – and can be white, silver, pink, gold, cream, and any combination of these basic colours, including overtones of the various colours of the rainbow displayed in the pearl nacre of the oyster shell itself.

Biologically, under the right set of circumstances, almost any shelled mollusc can produce some kind of pearl, however, most of these mollusc pearls have no lustre or iridescence. The great majority of mollusc species produce pearls which are not attractive to look at, and are sometimes not even very durable, such that they usually have no value at all, except perhaps to a scientist, a collector, or as a curiosity. These objects used to be referred to as “calcareous concretions” by some geologists, even though a geologist would still consider them to be pearls. Valueless pearls of this type are sometimes found in edible mussels, edible oysters, escargot snails, and so on. The GIA and CIBJO now simply use the term ‘pearl’ (or, where appropriate, the more descriptive term ‘non-nacreous pearl’) when referring to such items and, under Federal Trade Commission rules, various mollusc pearls may be referred to as ‘pearls’ without qualification.

A few species produce pearls that can be of interest as gemstones. These species include the bailer shell Melo (genus), the giant clam Tridacna, various scallop species, Pen shells Pinna (genus), and abalone's. Another example is the conch pearl (sometimes referred to simply as the ‘pink pearl’), which is found very rarely growing between the mantle and the shell of the queen conch or pink conch, Strombus gigas, a large sea snail or marine gastropod from the Caribbean Sea. These pearls, which are often pink in colour, are a by-product of the conch fishing industry, and the best of them display a shimmering optical effect related to chatoyance known as ‘flame structure’.

Somewhat similar gastropod pearls, this time more orange in hue, are (again very rarely) found in the horse conch Pleuroploca gigantea.

The largest pearl known was found in the Philippines in 1934. It is a naturally occurring, non-nacreous, calcareous concretion (pearl) from a giant clam. Because it did not grow in a pearl oyster it does not have the traditional pearl surface, instead it has a porcelain-like surface, in other words, it is glossy like a china plate. Other pearls from giant clams are known to exist, but this is a particularly large one. The pearl weighs 14 lb (6.4 kg) and was supposedly first discovered by an anonymous Filipino Muslim diver off the island of Palawan in 1934. According to the legend as it is currently told, a Palawan chieftain gave the pearl to Wilbur Dowell Cobb in 1936 as a gift for having saved the life of his son. The pearl had been named the “Pearl of Allah” by the Muslim tribal chief, because it resembled a turbaned head. Another even more elaborate legend says that this object is actually the Pearl of Lao-Tzu, a cultured pearl created with a carved amulet and then supposedly progressively grafted into several giant clams, before supposedly being lost due to a shipwreck in 1745. This legend has been discredited, however, because this pearl is indeed the product of a giant clam, Tridacna gigas, which cannot be grafted. This means that the pearl is a whole pearl, not a fictional pearl.

It should be noted that whole pearl technology is only a 100 years old.

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