Labradorescence — the blue flash in labradorite — is caused by light interfering between very thin alternating layers inside the feldspar. It is directional, which means a strand will always have a mix: some beads flash strongly, others look grey. A strand where every bead flashes identically is a sign of treated or synthetic material.
This is natural material from Madagascar. Labradorite is a feldspar and moderately soft, so it will scratch against metal; store it separately from harder stones.