Rock-butter, an impure alum efflorescence of a butter-like consistency found oozing from some alum slates.
Rock-butter
Chambers's Encyclopaedia, Volume 8: Peasant to Eoumelia, p. 755
Source scan(s): p. 0766
Rock-butter, an impure alum efflorescence of a butter-like consistency found oozing from some alum slates.