Rock butter
Soft mineral substance
From Wikipedia, the free encyclopedia
Rock butter (also known as stone butter) is a soft mineral substance found oozing from alum slates.
It consists of native alum mixed with clay and oxide of iron, usually in soft masses of a yellowish white colour[1] with translucent edges,[2]: 307 occurring in cavities and fissures in argillaceous slate.
This substance hardens when exposed to air, but softens if the air is humid enough.[3]: 28 The texture is sometimes described as "greasy".[2]: 307
It was referred to as "rock butter" in English as early as 1816.[2]: 306–7
It has been recorded in various locations around the world, including Hurley[4] and Paisley in Scotland; Bornholm, Denmark; Bad Muskau, Germany; and along the Yenisey in Siberia.[2]: 307 An 1837 article noted that at the "Kiffhäusen" stone quarries in Germany, the workmen called it steinbutter and ate it spread on bread.[5]: 37
There have been reports of people eating rock butter in various parts of the world, including Siberia,[3]: 28 Germany, and Austria.
