Schorl-rock, and Schorly granite.
"The Student's Elements of Geology"
Sir Charles Lyell
It was not till fourteen years after that the body of Clarke was found, and Mrs. Aram declared that her husband and Housman had murdered him; Housman turned King's evidence, and Aram was hung on 16th August 1759. Roche hermitage in Cornwall occupies a spire of rocks of Schorl that shoots 100 feet above the surrounding moor.
"Castles and Cave Dwellings of Europe"
Sabine Baring-Gould