MKM design necklace spinning India glass beads vtg caged pewter adjusts 19” RARE

This has a certain weight to it and is one of those necklaces that seem indestructible. Recently one of this designers necklace sold in the UK for €60., And this one is much rarer because the beads spin inside the encased pewter circles. Great for a fidgety necklace. Reminds me of the Greeks, my ancestry that carry the worry beads. If you know the name of this gemstone please share, thank you. Some of their necklaces are sterling silver but I didn’t see a 925 mark on this one. I believe it is India glass beads