Pearls can be produced by variety of organisms like sea molluscs. Also, they can be produced by fresh water mussels, or occasionally by snails too. Some of the varieties of pearl-producing oysters are:
- Black lip pearl
- Akoya pearl oysters
- Freshwater mussel
- Large winged pearl
- Golden Lip pearl or a white lip pearl
Around an irritant, concentric layer of Calcium carbonate is deposited. This can be a mantle lobe piece or few other materials.
The mantle lobe only can secrete nacre. If a mantle lobe piece is introduced by any accident into the oyster tissue, the oyster will form a bag which is known as “pearl sac”. This sac will secrete the nacre all around the irritant for making the pearl.
Few natural pearls may have quite unusual type of shapes and are often called as “baroque” pearls.
Both freshwater and saltwater pearl consists of the similar material and may form in “baroque” shape.
Only if you are very much familiar with typical characteristics of pearls from a specific source, then only you can find out whether a pearl was freshwater or saltwater in origin, otherwise it would be extremely difficult to identify.
One of the most common varieties of freshwater pearl available in market is Chinese freshwater baroque, few of which are crankily and have appearance of crisped rice.
In recent years, these pearls were very popular as they cost dramatically lesser as compared to Akoya cultured pearls.
Mostly oysters and mussels will be induced for making pearls. The results are termed as “cultured pearls”. Almost 90 percent of the pearls that are sold in the market are cultured pearls.
If you try to break a pearl and open it then you will find that it consists a bead that is covered by thin layer of material called nacre.
The culturing process too involves inserting small mantle lobe piece and bead is made from the pearl shell’s mother into tissues of pearl-producing mollusk.
These mollusks treat the bead as certain irritant and mantle lobe tissue starts depositing nacreous coating on it.
The blister pearls generally form on the interior of the pearl shell’s mother.