Birth of a pearl —  nature’s perfect gemstone

Pearls are a wonder of nature, a gemstone that is perfect just the way it is produced, needing no cutting and polishing like other gems

Just like masons build skyscrapers with layers of brick and mortar, a certain variety of molluscan bivalves or oysters produce pearls with layers of a substance it secretes

Pearls grow within the soft tissue of oysters. When a grain of sand gets lodged inside the oyster, it secretes a protein called nacre in layers over time, forming a pearl

Pearls usually come in the shape of a sphere, oval, or teardrop. At times, they can also look like a button or half sphere. But it’s the perfect spheres that are highly valued

A researcher, Lara Otter, looked at a pearl’s cross section under a microscope and found it had 2,615 layers of nacre and took 548 days to form. No two pearls are alike

As each layer of nacre reflects part of the light that falls on it, the pearls appear to shine; metals like sodium give it various shades of colour

Light passing through each layer of the nacre is partially reflected and partially absorbed, giving a pearl its irradiance

As different layers reflect back, the pearls acquire their characteristic lustre: white, cream, yellow, red, green, blue and even black

When all the incident light is absorbed, the pearl appears black, and the black ones are a rarity having high market value

Most of the pearls sold in the market today are cultured and are not naturally formed. Natural pearls that come from water bodies and seas are scarce and highly priced

The Indian ocean, East Asia and the Pacific region are studded with pearl culture farms where most of the pearls that we see in jewellery shops are produced

Cultured pearls are formed by putting tiny spherical beads made from shells into the oyster. This irritant makes the oyster secrete nacre, forming the pearl

Climate Change has emerged as a major threat to pearl oysters. With oceans warming, the normal function of the oyster is impeded due to heat stress

With oceans warming, seawater absorbs more carbon dioxide which results in acidification of the seas. With the water more acid, oyster shells get eroded faster

Scientists say the oyster would then divert significant nacre resources to fix their shells, rather than build pearls