Some gneiss I found! It was being used as part of a path. Note the alternating dark and light layers. The dark layers are composed of minerals such as hornblende (mafic minerals, containing more magnesium and iron), while the light layers are made of minerals like quartz and feldspar (felsic minerals, containing more oxygen, silicon, potassium, aluminum and sodium).
Gneiss forms at high temperature and pressure during mountain building. Any sedimentary or igneous rock can be metamorphosed to gneiss. The rock that is metamorphosed is called the protolith.