Vintage white onyx or agate bead necklace 19" long

This necklace is stunningly beautiful. It has round shaped white beads, gold tone spacer beads, and in the front, semi translucent white swirled roundels. I have tested the beads and they are gem and not glass. That said, I don't know if they are white onyx or a white agate (the two are closely related) There is a barrel closure. It is approximately 19" long - princess length.