I think they are cultured freshwater pearls. Some of the pearls are button shaped, or sometimes called rondel shapes.
Pearls are organic gemstones formed inside mollusks, and while some are sold untreated, many undergo post‑harvest treatments to improve color, luster, or uniformity. These processes are common in major producing countries like Japan and China, and are often considered standard in the trade. Treatments include things like washing, dyeing, bleaching, and there are others.