Need help identifying this rock

This black rock was found in the central Philippines in an island called Negros Occidental. The guy who found it said he had never seen a rock like it before and thought it to be rare. He conducted tests on the strength of the rock by hammering it and striking it with a pickaxe to see if it would break. He said it was extremely hard but he was able to split a portion of the rock. You can also see dents on the surface from where the pickaxe made contact. The shard that broke off was used to cut glass and apparently it worked.

I'd appreciate any help you can offer in regard to identifying this thing, as you can tell I know almost nothing about rocks but I thought I'd ask here to help this guy out. He seems convinced that this rock has great value. My guess is that it's some sort of igneous rock due to the volcanic nature of the Philippines.