Freshwater pearls are the most common non synthetic pearl that are available and are produced by mussels not oysters. They are cultured which means that the mussels are farmed and the pearls are encouraged to form in a controlled environment.
Up to 50 pieces of tissue can be grafted into a single mussel producing a high volume of pearls but because of the high volume and irregular shaped tissue grafts, the pearls are usually irregular in shape and the nacre can be dull and patchy. Each batch is grown over a period of about 6-12 months but this depends on the quality of the pearl that is wanted.
As a general rule, the longer the pearl is inside the mussel the thicker the nacre, the larger the pearl and the better quality it will be. Freshwater pearls are rarely found larger than around 9mm. Naturally the colour of freshwater pearls can vary from white to pastel pinks, peaches and lavenders although they are often dyed or bleached to make them more attractive.
These are the least expensive type of pearl but can be just as beautiful in their own way! A great was to enjoy pearls on a budget! Look out for potato shaped pearls or rice crispy shapes. I would avoid the really heavily ringed pearls though as they tent to trap dirt and can look nasty very quickly.