alum shale
Noun
Meaning
A variety of shale or clay slate, containing iron pyrites, the decomposition of which leads to the formation of alum, which often effloresces on the rock.
Source: Webster's dictionaryNoun
A variety of shale or clay slate, containing iron pyrites, the decomposition of which leads to the formation of alum, which often effloresces on the rock.
Source: Webster's dictionary