I made this super long necklace with some lovely green agate ovals, some "wire" beads, and gunmetal chain. It reaches nearly to my waist.
I have also made a shorter chain section that I can clip in, to turn it into a shorter, double strand piece, giving me a bit more versatility.
The agate were purchased at my local gem show, and cost me $10.00 for a strand of about 12 beads. They are around 50mm long, so are a great feature bead.