Rock butter (also known as stone butter) is a soft

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

substance found oozing from alum slates. It consists of native alum mixed with

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

and oxide of iron, usually in soft masses of a yellowish white colour, occurring in cavities and fissures in argillaceous slate.

Notes

References

* http://dict.die.net/rock%20butter/—has information from

Webster's Revised Unabridged Dictionary ''Webster's Dictionary'' is any of the English language dictionaries edited in the early 19th century by American lexicographer Noah Webster (1758–1843), as well as numerous related or unrelated dictionaries that have adopted the Webster's ...

(1913)
Rock Butter
from the

U.S. Bureau of Mines For most of the 20th century, the United States Bureau of Mines (USBM) was the primary Federal government of the United States, United States government agency conducting scientific research and disseminating information on the extraction, proce ...

' '' Dictionary of Mining, Mineral, and Related Terms'' (1996), online at the

Hacettepe University Hacettepe University is a leading state university in Ankara, Turkey. It was established on 8 July 1967. It is ranked first among the Turkish universities by URAP in 2021. The university has two main campuses. The first campus is in the old t ...

Department of Mining Engineering website. * * Minerals {{mineral-stub