Lava rock in reef tank?

[Beefcake]

Found some lava rock while digging through some stuff I had laying around when getting ready to set up my 180. Would it be safe to use? I've seen somewhat mixed answers online.

[Origami]

I'd be cautious using it. If it's synthetic lava rock (made for commercial purposes), it may have additives that may leach and be toxic to your tank. However, a lot of natural lava rock is safe. However, you may have difficulty keeping it submerged because of trapped air in the rock.