Contact between granite (light-coloured rock) and hornfels (dark-coloured striped rock) on the island of Ile Milliau near Trébeurden in Brittany, France. The granite is the porphyritic La Clarté variety of the Ploumanac'h granite pluton of Carboniferous age. The hornfels is a contact metamorphic rock that was formed by the heating of older sedimentary rock when the hot granitic magma intruded into the sedimentary rock. The hornfels contains the mineral andalusite. The blackest bands of the hornfels also contain the mineral cordierite.