White marble like irregular bead necklace vintage costume jewelry ll2521

I bought this necklace thinking it was white agate or marble of some sort but it is plastic with inclusions similar to what you would find in white marble or onyx. The beads are elongated slightly swirled rectangular cut with squat round smaller white bead spacers. There are also metal spacers that look pewter in color. They are actually that color from age. It is 19 inches long and in excellent condition. Nice for summer.