rock butter
Noun
Meaning
rock butter (uncountable)
Native alum mixed with clay and iron oxide, usually in soft masses of a yellowish-white colour, occurring in cavities and fissures in argillaceous slate.
Noun
rock butter (uncountable)
Native alum mixed with clay and iron oxide, usually in soft masses of a yellowish-white colour, occurring in cavities and fissures in argillaceous slate.