Double best Strand Pearl with .925 Statement Clasp Necklace

Product Name: Double best Strand Pearl with .925 Statement Clasp Necklace
This was my grandmother's necklace and it looks every bit of 1920's glamour. I honestly don't have a lot of information about this piece. The pearls range from about 6mm for the larger strand and 4 mm for the smaller strand. I THINK they are freshwater, I am not a jeweler, but my research online indicates the best smaller size would be the freshwater less valuable pearls and they are probably treated in some way because they are lovely silver color. The clasp is really what makes this necklace in my opinion. It is stamped sterling and is encrusted in marcasite and oval gemstones, probably white topaz. All marcasites are present- in excellent condition.