Pearl

Colour and varieties

Colour-body colours of pearl can be broadly classified as white, golden, grey, brown(Chocolate) and black. In addition, there may be various iridescent tints including pink, green, blue and lilac contributing to the overall colour of the pearl.
Pearls used in jewellery fall into two categories:-
Natural- produced entirely by natural categories Cultured- Artificially initiated and farmed.

Marine (saltwater)
Freshwater

Pearls are among the earliest of gem materials used for personal adornment. Created by soft-bodied animals which secrete a hard outer shell of calcium carbonate around themselves and live in fresh- and salt-water locations throughout the world, pearls need no cutting to reveal their beauty.

Lustre- the unique lustre of pearl is a complex effect, quite different from the lustre of polished gemstones. It is produced partly by the surface reflection of light and partly by a subtle iridescence. The resulting combined reflection effect is known as the ‘orient’ of pearl.
Weight- a unit of weight common used for natural pearls is the pearl grain: 1 pearl grain = 0.25ct. Momme is a unit of weight used for cultured pearls: 1 momme= 3.75g
Pearl is one of the birthstones for June.
As an emblem of modesty, chastity and purity, the pearl symbolizes beauty, love, success, and happiness. They often symbolize a happy marriage and in many countries are used as a wedding gift.

The origin of pearls

Pearls are produced in water-dwelling animals, in certain types of shellfish known as molluscs. The most important pearl-producing molluscs are saltwater oysters and freashwater mussels. These animals belong to a subgroup of the molluscs, known as bivalves, in which the shell consists of two hinged parts. Pearls can also occur in gastropods such as the rare conch pearls—these will be coverd in the IDT Graduate Gemologist Diploma Course.
The familiar round pearl forms inside the body of a mollusc; these are called cyst pearls. Blister pearls form on the inside of the shell and need to be sawn away from the shell to release them. The unique lustre of a pearl is created by the nacre layers that cover the pearl. The nacre layers are deposited by the mantle of the oyster; this is the soft tissue of a mollusc that also creates the mother-of-pearl inner surface of the shell. In natural pearls, pearl formation may be related to damage of the mantle caused by parasites, disease or attack by predators. In cultured pearls, the process involves using a section of the mantle of another oyster with or without a bead nucleus; this is called tissue nucleation. More information about the formation of pearls and the different molluscs involved is discussed in the IDT Graduate Gemologist Diploma course.

Natural pearls

Naural pearls possess a concentric structure made up of layers of nacre. These layers are affected by various factors including seasonal growth, temperature change and food supply.

Localities

Saltwater (or marine) natural pearls can occur in a wide range of localities. In the past the most important natural pearl fisheries were in the Central Americas, the Persian Gulf and the Gulf of Manaar (between Sri Lanka and India). Commercial fishing for natural pearls is now virtually nonexistent due to fundamental changes in ocean ecosystems and to economic circumstances. Although, natural pearls are still occasionally found in these areas, as well as in oysters in the area farmed for the pacific ‘South Sea’ cultured pearl; other localities include the Red Sea, the Gulf of Mexico and off the coast of Venezuela. The rarity of natural pearls often means that necklaces are graduated because of the difficulty in matching their sizes.
Other natural marine pearls such as the non-nacreous conch pearl are covered in the IDT Graduate Gemologist Diploma Course. Natural freshwater pearls were fished from rivers in most European countries, but little or no fishing is now carried out although natural freshwater pearls may still be found in Scotland, Letland and North America.

Cultured pearls

There is now an enormous market in cultured freshwater and saltwater pearls. The insertion of objects such as figures of Buddha between the shell and mantle of molluscs, in order to obtain a covering of nacre, has been practised by the Chinese since the thirteenth century. Although, the process of obtaining cultured blister pearls was not patented until 1896 by Kokichi Mikimoto in Japan. Round cultured pearls from Japan first appeared on the market around 1905.