Antique Satin Spar Necklace, 1920s, 15-1/2 to 17 inches long

Vintage white necklace with beads that I believe are satin spar. They have a matte satin surface and the white varies in shades and iridescence on each stone. 
The necklace is adjustable fitting from 15-1/2 inches to 17 inches with adjustable hook and chain.

The necklace is in very good condition. One bead in the front may have a crack in it, or it could just be the coloring inside of it. Metal is tarnished.