This is basically a bar of purple glowing Tritium
(You can only see it in the dark, yet it last for over 20 years)
Crafted with pieces from a very old clock, bras, some wood and all onto a chain of silver.
This is a Energy Core for a plasma/Tesla weapon, and because these cells are so expensive, they are often used in jewelry, like this one.
If someone wants to buy this, it is now broken Dx I accidental the wood.