An aggregate of one or more MINERALS rather large in area. The three classes of rocks are the following: (1) Igneous rock - crystalline rocks formed from molten material. Examples are granite and basalt. (2) Sedimentary rock - A rock resulting from the consolidatrion of loose SEDIMENT that has accumulated in layers. Examples are sandstone, shale and limestone. (3) Metamorphic rock - Rock that has formed from preexisting rock as a result of heat or pressure.