The three types of rocks are igneous, sedimentary, and metamorphic. Igneous rocks form from the cooling and solidification of magma or lava and include examples like granite and basalt. Sedimentary rocks develop from the accumulation of sediments, often containing fossils and layered structures, with sandstone and limestone being common examples. Metamorphic rocks arise from existing rocks that undergo changes due to heat, pressure, or chemically active fluids, which alter their mineral composition and structure, as seen in marble and schist. These rock types illustrate the dynamic geological processes that shape the Earth.