The pendants of this medieval necklace are real quartz crystals. They are fixed by a black waxed rope; the length is adjustable.
This jewellery is a one-of-a-kind piece. Can be repeated on request, but keep in mind that it would never look exactly the same.
Please let me know if you would like to see more photos of it, or if you have any questions.
P.S. There is a similar type of earrings to this necklace, which can make it a nice kit together (see the last photo in the gallery). The link to the earrings - https://www.bydarktales.com/product-page/quartz-crystal-earrings