What does Alum shale mean?

Alum shale meaning in General Dictionary

a number of shale or clay slate, containing iron pyrites, the decomposition which contributes to the forming of alum, which frequently effloresces from the stone.


Alum shale meaning in General Dictionary

many different shale or clay slate, containing iron pyrites, the decomposition that results in the formation of alum, which effloresces regarding the rock.