Butter

Butter (ROCK), or HALOTRICHITE, a mineral which may be regarded as a variety of Alum (q.v.)—an iron alum, appearing as a pasty exudation from rocks that contain alum or its constituents, particularly alum-slate and other schistose rocks. Rock butter occurs at Hurlet alum-work, near Paisley, Scotland, and in a number of places on the continent of Europe. It is not unlike butter in colour, varying from yellowish-white to sulphur-yellow, is silky-fibrous, and has an inky astringent taste. It is rather greasy to the touch, and is easily broken in pieces.