) is an earth science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which they change.
This rock can be weathered and eroded, and then redeposited and lithified into a sedimentary rock, or be turned into a metamorphic rock due to heat and pressure that change the mineral content of the rock which gives it a characteristic fabric.
The sedimentary rock can then be subsequently turned into a metamorphic rock due to heat and pressure and is then weathered, eroded, deposited, and lithified, ultimately becoming a sedimentary rock.
Sedimentary rock may also be re-eroded and redeposited, and metamorphic rock may also undergo additional metamorphism.
All three types of rocks may be re-melted; when this happens, a new magma is formed, from which an igneous rock may once again crystallize.
The majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth.
Geologists also study unlithified material, which typically comes from more recent deposits.
These materials are superficial deposits which lie above the bedrock.
Geology also plays a role in geotechnical engineering and is a major academic discipline.
There are three major types of rock: igneous, sedimentary, and metamorphic.
The rock cycle is an important concept in geology which illustrates the relationships between these three types of rock, and magma.
When a rock crystallizes from melt (magma and/or lava), it is an igneous rock.