A mineral is a naturally occurring solid of inorganic origin, with a definite chemical composition and in most cases an ordered atomic arrangement. Compositions range from pure elements like gold (Au), diamond (C), or native copper (Cu) to simple oxides (SiO2 – quartz; TiO2 – rutile) or carbonates (CaCO3 – calcite) to highly complex silicate minerals (e.g., tectosilicate such as K-bearing feldspar KAlSiO3). The latter dominate most parts of the solid Earth, the exception being the core which is composed mostly of Fe-Ni alloy. Most minerals are crystalline, but some, like chalcedony or opal, are amorphous. Assemblages of different minerals compose a rock.