To me (not an expert) they look like freshwater pearls because from the photo, some of them look a little flattened or "eggy." Freshwater pearls (except for some of the newer, large bead nucleated ones) don't have a round nucleus inserted to form around so they often have that shape.
It's hard to tell exactly what you have there, though. Can you take some photos on a white paper towel, preferably in natural filtered light, such as from a covered patio or indoors by a window? Then we could get a better look.
Also, how many mm are the pearls? How long is the strand? What metal is the clasp made of? How would you describe the color?