Secret story of pearls

SCIENCE FOR YOUTH

By Hiya Islam

science

Pearls, nature’s cryptic creation, have long amazed us with their splendor. Rich in beauty and value, these are confined inside oysters lurking in the depths of the ocean. Oysters are one of the members of the phylum – Mollusca, the same group where mussels, clams, snails, slugs, squids and even octopuses belong. Pinctada maxima, a pearl oyster, is one such mollusk we are indebted to for the lustrous beads in our lives.

Far away from the gleaming water on the surface, the birth of a pearl takes place purely by chance. It begins as foreign matters as a parasite finds its way into the oyster. The oyster is made up of an outermost shell protecting the stomach, heart, gills, mantle and other vital organs. The mantle produces a response as a defense mechanism – the secretion of nacre or mother-of-pearl. Nacre is composed of aragonite (a crystalline form of calcium carbonate) and conchiolin which is a protein and is used in making the shell. Layer after layer of this nacre is deposited on the intruder resulting in coveted gems waiting to be discovered by the hands of greedy men. However, not every pearl that forms is perfectly round. Misshapen beads are called baroque pearls. They are nonetheless in demand for jewelry-making. Despite being oddly shaped, it has been possible to categorise them into teardrop, rice, cross, twin and keshi pearls.

Using this knowledge, oyster farmers can now culture pearls. Pearl culture involves a little ‘push’ from the humans to induce pearl growth. Oysters are bivalves. Their shells are snapped shut when alive and open when dead. The shells are carefully pried open a few centimeters. Next, a nucleus (small part of the shell) and a small piece of mantle tissue are surgically inserted into a mature oyster. The mantle tissue stimulates release of nacre to be coated on the nucleus that acts as foreign matter. Nucleated oysters are returned to their habitat only to be picked up again 1-3 years later. Progress of pearl growth is monitored by use of X-rays. Back at the pearl farm, precious pearls are extracted by cutting oysters’ flesh. Care is taken not to harm the pearl-producers. Healthy oysters are reseeded to make more pearls.

Cultured pearls are no different than natural pearls as they develop in the same mechanism. They only differ in price. In the wild, there is roughly 1 in 10,000 chances of finding a pearl in an oyster. Compared to that, pick up any oyster in the farm and the luck is in your favor. Pearl value is established by determining if it’s natural or cultured and its luster, shape, size and color.

To distinguish between a real gem and an imitation wannabe, rub it on your teeth. If it feels gritty, it’s the gem! But of course, a closer look with a magnifier reveals the true nature.

Hiya Islam is a student of BRAC University.

 

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