Gneiss wani nau'in dutse ne na metamorphic wanda ke da siffa ta banded ko foliated kamanninsa, wanda shine sakamakon sauye-sauye na ma'adanai daban-daban. Yawanci ana yin shi ta hanyar metamorphism na yanki na dutsen da aka rigaya, irin su granite ko shale, kuma galibi yana kunshe da ma'adanai irin su quartz, feldspar, mica, da hornblende. Kalmar "gneiss" ta fito ne daga kalmar Jamusanci "Gneis," wanda ke nufin "mai kyalli" ko "mai haske."