Vintage Black Glass or Stone Bead Necklace

Beautiful vintage beaded necklace. Probably circa the 1970s or so. Black beads towards the center that resemble puka shells to me in groups of three with knots in the strand between the groups. The rest of the necklace is the round beads. Looks and feels like glass or stone or maybe shell. Measures about 24" long total. No marks or labels. 
Excellent vintage condition. Nothing to note.

Please note: These are vintage, preworn and/or preloved items. I do my utmost best to list any issues, but signs of wear should be expected, and there are occasionally small things I won't deem worthy of note. Please feel free to send me a missive with any questions. I'm truly happy to help in any way possible and I'm always up for a chat. Any accessories shown, including crinolines, are for display only, not included unless otherwise stated.