looks like lapis lazuli or azurite
lapis lazuli is commonly used in witchcraft and it seems to be a healing stone to relieve depression as well as unlocking the third-eye (which connects with spiritual abilites), and it blocks psychic attacks...
if you want more properties:
http://www.controverscial.com/The Magic of Rocks and Stones - Lapis Lazuli.htm
And Azurite is known for unlocking the third-eye in spirituality, helps with circulation, removes negative thought patterns...
more:
https://www.energymuse.com/azurite-meaning
based on the properties i feel like it'd be lapis though..
He seems to know about gemstones and spirituality to be wearing one a lot..
Which gives me hope that I might not actually be going crazy thinking that RM and him might have a spiritual connection and might be more aware than the majority of us
Hopefully all good things spiritually-related though.. -cough-
But whatever gemstone it is it's definitely charged