When most people think of pearls they picture perfect large round spherical gems, creamy white in colour with a shimmery iridescent surface. The reality is that pearls are usually irregular in shape, each one is different and to find one that is completely round is almost unheard of, let alone a whole string that are all identical. Natural pearls are the rarest and most highly valued variety, but nowadays most pearl jewellery is made from cultured or farmed pearls, which are grown on pearl farms across the world by inserting a bead nucleus inside an oyster or mussel shell to encourage the formation of a pearl. Aside from whether a pearl has formed naturally or been farmed the other major varieties are the saltwater or freshwater pearl, each of which have their own qualities.

Saltwater pearls are found in pearl oysters which live in the ocean, and produce the classic round white or cream pearls that have remained so desirable and sought after throughout history. Comparing farmed pearls, saltwater pearls are often rounder than those grown in freshwater farms as they are made by inserting a bead into the oyster to encourage the shape. The Japanese Akoya is the most popular type of cultured saltwater pearl and is much sought after for its large size and relatively regular shape, meaning that this type usually costs more than cultured freshwater pearls. It is still possible to find natural saltwater pearls in the ocean, but they are much less common nowadays because of increased levels of pollution.

The most common type of pearl available today are freshwater pearls, which are mostly produced in China using freshwater mussels and come in a huge variety of shapes, sizes and colours. The natural colours of freshwater pearls are various shades of white, pink, cream and lilac but they are available as jewellery dyed in every colour of the rainbow. It is easier to farm freshwater pearls than saltwater, making them cheaper to buy as jewellery, though it is rare for them to be perfectly round and a necklace of cultured freshwater pearls will hardly ever be all the same size and shape.