Vintage black tourmaline/white marble beaded necklace

Wonderful vintage beaded necklace with black & white stones. The white beads may be marble? They have slight marbling & a hint of shimmer. I think the black beads are black tourmaline - they are not all 'perfect' & upon close inspection they have some coloring to them & a slight sheen (where as onyx would be jet black.) It is a heavy piece, and cold to the touch. The string is also knotted between each black bead. Can be worn as bracelet as well- as shown 😊