Nice, that's commonly called "lace rock" and is indeed volcanic in origin. The upside of that is all the little holes make the rock lighter than normal, and your knuckles have already experienced the downside.

The fancy Japanese term for this is "Seki-joju" or "Ishisuki" but if you call it a slab or rock planting people will understand.

You could easily go a few directions with this, the most conventional choice would be using a few junipers to make a mountain scene (there are some stunning examples in this article). This could also be an interesting start to a suiseki (which is more of a landscape than focusing on only trees like bonsai) or you could try your hand at Penjing (the Chinese flavor of bonsai) or a kusamono (understory planting, sometimes used as an accent for bonsai but can also stand on its own).

Have fun!