Grown in mussels rather than oysters, usually solid nacre, and by far the best value entry into real pearls.
Freshwater pearls are cultured in mussels, overwhelmingly in China, and account for the large majority of pearls sold by volume worldwide. They are the reason real pearl jewellery is affordable at all.
Most freshwater pearls are grown by inserting a small piece of mantle tissue rather than a bead nucleus. The mollusc then deposits nacre around it, producing a pearl that is often solid nacre throughout rather than a thin coating over a bead. That makes them durable and means they wear well over decades.
A decent strand of 7–8 mm freshwater pearls runs roughly £80 to £250. Larger, rounder, better-matched strands with strong lustre reach £400 and beyond. Compared to any other real pearl, this is remarkable value.
A first pearl purchase, everyday wear, gifts, and anyone who prefers baroque shapes to classical roundness. Because the nacre is thick, they tolerate regular wear better than thin-nacre Akoya.
On dyeing. Black, chocolate and vivid colours in freshwater pearls are almost always dyed. That is not a problem in itself, but it should be stated plainly by the seller. A "black pearl" at a freshwater price is a dyed freshwater pearl, not a Tahitian.