Crumblestone

Crumblestone was a very brittle type of rock.

History
Crumblestone was notorious for how brittle and therefore dangerous it was to miners and travelers in the Underdark.

Properties
As mentioned above, crumblestone was brittle, it turned into powder when weight was applied, for example when a flying creature or a climber stepped on it. This might cause climbers to fall and die, but was mostly harmless for a flying creature. The larger problem was something different. The problem lay in the fact that this rock was part of an equilibrium that broke once the crumblestone broke, which might cause an entire cave-in, if the amount that broke away was sufficient.

Applications
A suggest use of the spell stone metamorphosis was to turn crumblestone into something more stable like granite when encountered.

Production
Crumblestone was a magimorphic rock. This meant that this type of rock came into being by magic and not by nature.