Source special issue: classic-minerals-of-northern-england, PDF page: 82. Label: Fluorite penetration twin, 6 cm, from the Boltsburn mine, Rookhope, Weardale, Durham (LG-63); shown in daylight (left) and in incandescent light (right). This is a pre-1860s specimen, though its history has been lost. Ex Ralph Sutcliffe col-lection; Joe Budd photo.

Origin: Boltsburn mine, Rookhope, Weardale, Durham