The size of these coin pearls is 10-11mm. These freshwater coin pearl beads may be some lumps and bumps, but the luster makes up for it. Thick nacra! Yep, thick, I tell ya. Freshwater coin pearl beads are created when a small flat disc shaped shell, instead of a round bead, is inserted into the oyster or more commonly these days, mussel. Most of these pearls are farmed in rivers, lakes or streams. The result is a a fabulous flat disc shape pearl. Our freshwater coin pearl beads are picked by their luster and size.