Igneous Petrology includes the study of igneous rocks (extrusive and intrusive) formed by the cooling and hardening of molten rock. Since the formation of the Earth 4,56 billion years ago igneous activity has occurred in a variety of tectonic environments. Melting and formation of magma took place various conditions resulting in differentiation and the formation of wide variety of rocks. By studying the mineralogy, geochemistry, isotope composition and phase relations, we can interpret the story as to how the rock was formed and say something about the tectonic setting where it was formed.
Sedimentary petrology is the classification and study of sedimentary deposits/rocks. This study is the basis for understanding sediment transport and deposition processes, as well as shedding light on the environmental setting where the sediments were formed. It is also important to examine the metamorphosis of sediments or sedimentary rock to a different sedimentary rock through, for example, cementing, compaction, mineralogical and chemical transformation.
There are two main branches of sedimentary petrology. One branch deals with clastic rocks which are primarily composed of particles of erosion, like clay/mud, sand, gravel and coarse material. The other deals with carbonates (limestone and dolomite) which are made up of calcium carbonate and calcium-magnesium carbonate. In many cases, the origin of these settings the shell remains from various life forms that lived in the sea or on the bottom. Carbonates may also be formed by evaporation of salt water in the dry environments.
Metamorphic rocks are formed when rock undergoes varying degrees of re-crystallization due to changes in pressure, temperature conditions and changes in composition of the Earth's crust during liquid phase. This setting allows for reactions between the original minerals and results in the formation of new minerals. The physical conditions on the earth during rock metamorphosis can thus be inferred. By combining this data with the dating of the various minerals, we can gain important knowledge about the role of particular rock types in the formation of land.