Niter
Niter Deposits give Saltpeter. They appear close to mountains (?) and can be mined. Picture shows a niter deposit at Ilshenar, close to the Compassion shrine at the passage to Castle Blackthorn.
When mined they will get smaller and smaller till they vanish. The order of size descriptions, from largest to smallest are: Gigantic, Massive, Huge, Large and Small.
They can not be picked up.