Materials

The rocks and minerals that make up the solid Earth, catalogued by two real classification systems rather than one: rocks by the standard igneous, sedimentary and metamorphic origin used throughout geology, and minerals by the Nickel-Strunz and Dana chemical-composition classes used throughout mineralogy. Every material entity carries a hardness (Mohs scale), a formation class describing how it forms, and, for minerals, a chemical formula where one is well defined. Belongs here: any naturally occurring rock or mineral substance the physical Earth is built from. Does not belong here: a physical process such as plate tectonics or erosion that shapes or produces these materials (Processes), or a phenomenon such as an earthquake or eruption that a material may be involved in (Phenomena).