Gneiss is a metamorphic rock often formed from high grade regional metamorphism, usually from pre-existing rock (known as the country rock). As the metamorphic processes are high grade, the original rock could have either been sedimentary or igneous. One of the most identifiable features of gneiss are its alternating dark and light foliations, known as banding, which are known as gneissic banding and composed of various dark and light coloured minerals. The dark bands are often comprised of mafic minerals such as iron and pyroxenes where as the lighter coloured bands are felsic in chemical composition, often comprised of potassium, aluminium or silicate minerals. This particular rock specimen is known as hornblende gneiss, as it is comprised mainly of the mineral hornblende, with the alternate light bands being almost completely quartz. The hornblende give this gneiss its over all dark colouration, These specimens were collected by staff from southern Norway and over all, is a coarse grained rock and can come in 3 optional sizes, each specimen will be supplied in a card tray with an information label.