Blood of Tohan
Black rock is the byproduct of forging demon steel from demon rock. Black rock is very brittle. When struck, it will splinter and form into dust. Even if tightly grip, it will tend to splinter and seep into the skin. This is one of the reasons it is rarely used in weapons. The other would be it’s toxicity to living creatures.
Black rock causes create irritation when it gets under one’s skin. It will rash and can break up into the blood stream, causing fatigue, dizziness, numbness, and aches. If inhaled or taken in the eyes, it can be somewhat dangerous, sometimes stopping breathing or blinding the person.
Even so, it can be formed into weapons (normally by demons who are immune to it’s effects). The process is similar to creating ceramic items.
Black rock has been used in the making of small explosives, and quite effectively.