Freshwater and saltwater pearls definitely have their differences. However, all pearls are created the same way.
It all begins when a small piece of sand or debris gets stuck inside the mollusk shell and is slowly coated by layer after layer of nacre, also known as mother of pearl. Eventually, the intruding particle is ejected back into the water as a finished, natural pearl.
Cultured pearls come from farms, and the technique of culturing pearls was developed by Japanese scientists in the early 20th century. The outside of a cultured pearl is still made entirely of nacre – which gives the pearl its natural trademark, iridescent luster. However, the core of the pearl is actually organic material which was purposefully placed inside the shell to produce a pearl in 6 months or less. What’s more, cultured pearls are very hard to distinguish from their natural counterparts, even with the help of scientific instruments. These days, natural pearls are rare and difficult to retrieve, so the vast majority of both saltwater and freshwater pearls are cultured in farms.
Saltwater pearls come from oysters that reside in, you guessed it, oceans and seas. They’re usually more round than freshwater pearls, which are often potato-like in shape. Different colours are common among saltwater pearls depending on where they come from. Soft pink is the natural hue, but steely grey and purple pearls are also found in Tahitian waters, and Australian seas are known for light grey, white, and slightly golden pearls. Pearls from the South Seas can also grow to be quite big but lack the surface quality and market value of, say, the Japanese Akoya pearl. It can generally be said that saltwater pearls are more expensive than freshwater pearls because they are rarer and harder to farm; storms in open water and oyster diseases are the culprits of many a lost pearl, and saltwater pearl operations are costly at the best of times.
Freshwater pearls come from mussels that live in rivers, streams, and lakes. They’re available in a wider variety of colours like white, cream, pink, lilac, and peach, but are also commonly dyed to produce a virtually limitless palette. Again, freshwater pearls aren’t usually as round as saltwater pearls, but they are still judged on the same criteria whether cultured or all-natural: roundness, surface quality, and size.
In summary, saltwater pearls are more expensive because of scarcity and cultivation issues, but freshwater pearls are often indistinguishable anyway. It has been found that specialists cannot, even with the aid of x-rays & ultrasound equipment, tell the difference between a freshwater and a saltwater pearl.