Rock

A rock is a naturally-occurring solid aggregate of one or more minerals, mineraloids or, in some cases, organic material. Sediments are the unconsolidated equivalent of these. Other related materials, including some man-made materials, are included within this categorization, along with the major classifications for meteorites.

Strictly, any naturally formed aggregate or mass of mineral matter, whether or not coherent, constituting an essential and appreciable part of the Earth's crust. Ordinarily, a consolidated or coherent and relatively hard, naturally formed mass of mineral matter; stone. In instances, a single mineral forms a rock, such as calcite, serpentine, kaolin, and a few others, but the vast majority of rocks consist of several minerals. It can include glasses and mineraloids eg. obsidian, or solid organic material, e.g., coal.

Reference: American Geosciences Institute