Lava rock is popular in planted aquariums due to it's rough texture its ideal for planting mosses on. It can also be used stacked upon one another to build the hardscape of your aquascape. Also creating caves for Shrimp and fish to hide in.
The appearance of the stone is gray with something of a blue tint through it. Furthermore, this type of rock often has calcite veins running through it. This, together with the erratic to sometimes sharp corners, ensures that the stone gets extra contrast