The hornblende schist, found in contact with the serpentine mass directly to the North (at Ogo Dour) and to the South (at Pentreath and Church Cove) is the metamorphic remnant of basaltic intrusives into the upper crust. It is typified by a schistose texture and visible crystals of black or dark green hornblende. Structural studies of the hornblende schist indicate that it has been subject to at least three stages of deformation. Folding of the schist at Housel Bay indicates that the formation was also subject to more than one subsequent stage of shear stress.