I would like to sell this necklace but can't remember its original description and the online store where I got it no longer carries it so I can't look it up that way. Blue Chalcedony comes to mind, but I'm not sure. Thank you!
My first guess with that rich a blue would always be Lapis Lazuli, Azurite is also a strong candidate and you can get Turquoise that dark but it's rarer. Unfortunately without rather destructive testing of a piece there's not a lot to tell the three apart in this sort of polished from.