- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
Ludlovian (Silurian) sandstones near Woolhope, Herefordshire, England, contain abundant biotite flakes, as well as conodonts and fish remains. Strata with similar bands of biotite in other localities of the Welsh borderland indicate a widespread occurrence. The source is thought to be Precambrian igneous and metamorphic biotite-rich rocks of the Malvern hills area.