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. A larger problem occurred when this rock was part of a delicate balance with surrounding stone, which was upset once the crumblestone broke and might cause a fall or even a cave-in.

Applications
A suggested 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 as a result of magic and was not natural.