Solid rock is formed by three main geologic process:
| Rock Classification | Origin |
| Igneous Rocks | Crystallized from molten state on surface or in the crust |
| Sedimentary Rocks | Deposited by water or wind, solidified by pressure of overlying units |
| Metamorphic Rocks | Recrystalized from previously existing rocks by heat and pressure |
Igneous rocks originate from melts deep in the crust. Some melts never reach the surface, but slowly solidify within the crust. Others reach the surface through volcanic eruptions, and rapidly cool.
Majority of sedimentary rocks formed in shallow seas. Sediment is derived by precipitation from sea water, or from suspended sediment carried in by the rivers. The pressure of the overlying sediment and the contained mineralized pore water eventually consolidate the sediment into rock.
Metamorphic rocks form from pre-existing rocks by the heat and pressure of burial in the crust. Heat, pressure, and contained pore solutions recrystalize the existing minerals into new minerals, and often result in a rock that is radically different from its parent. Other metamorphic rocks closely resemble their parent mineral composition.
