Gneiss is a type of metamorphic rock with a striped appearance due to layers of light and dark minerals. In this case, biotite, sometimes called black mica, is the dark mineral.

The gneiss, located on the top of the mountain, consists of mainly a biotite-quartz-feldspar gneiss interlayered with minor amphibolite gneiss and feldspar augen gneiss. Over a kilometer of land ...