it is so called as functional stone which canbe used be used safty in any places for its low radiation ,wind erosion-proof and durability, sound absorbing and noise lowering ,water absorbing and air humidity keeping ,dizzy light avoiding ,etc, in improving our environment and feelings.
lavastone is a common extrusive volcanic rock,it is usually gray to black and fine-grained  due to rapid cooling of lava at the surface of a planet.