Pearls are formed due to an immune response inside the shell of certain molluscs, which serves as a defence mechanism against a potential threat, such as a parasite or an outside threat that might injure the mantle tissue. A tiny piece of mantle tissue from a donor shell is being transplanted into the recipient shell, which causes the formation of a pearl sac, where the tissue deposits calcium carbonate. Pearls are considered feminine pieces of jewellery and are associated with the Moon and the planet Venus.
It is primarily described by the size of the pearls in millimetres (mm) rather than their weight. The larger the size, the higher the price, but the price jumps might be uneven when it comes to pearl sizes. Once the size reaches the scale of 8-9mm and above for the diameter, the prices tend to increase much more than the lower diameter ranges.
Pearls can come in round and oval shapes, and they could be pear-shaped or even misshapen. The latter ones go by the name of “baroque pearls”. Symmetrical spheres or symmetrical drops are among the most valuable pearl shapes. Pearl sizes typically range between 2-16 mm in diameter. This size solely depends on the type of mollusc where they are formed.
Good clarity would mean the pearls come with the characteristic pearly lustre, with sharp and bright reflections on their surface. They would be smooth and blemish-free, and a suitable layer of nacre would be present to increase durability.
Pearls come in various colours, from white to black. However, the natural colour results from a combination of several factors, such as the predominant basic colour of the pearl, one or more colours over tiling the body colour, and the play of lustrous colours. These latter ones could be a subtle combination of colours such as pink, green, blue or even silver, and they would change once you move the pearls in your hand.