Mineralogy and the formation of rocks

Minerals

Minerals are naturally occurring, inorganic substances with a definite chemical composition and crystalline structure.
Each mineral possesses unique physical properties like hardness, lustre, colour, and cleavage which helps in their identification.
More than 2000 minerals have been identified, but around 20 (such as quartz, feldspar, and mica) make up most of the Earth’s crust.
Mineral groups include silicates, carbonates, oxides, sulphates and organic minerals; each group has a specific chemical composition.

Igneous Rocks and Processes

Igneous rocks form from the cooling and solidification of magma or lava.
Intrusive igneous rocks, such as granite, form when magma solidifies slowly beneath the Earth’s surface. They show coarse-grained texture as they cool slowly allowing large crystal formation.
Extrusive igneous rocks, such as basalt, form when magma erupts onto the surface and cools rapidly. They exhibit a fine-grained texture due to the fast cooling, allowing little time for large crystals to form.
Certain igneous rocks, like pumice, contain vesicles which are cavities that result due to the escape of gas during eruption.

Sedimentary Rocks and Processes

Sedimentary rocks form from pre-existing rocks or organic material. The process of formation is broken down into weathering, erosion, deposition, compaction, and cementation.
Clastic sedimentary rocks form from the accumulation and lithification of mechanical weathering debris. Examples include sandstone and shale.
Chemical sedimentary rocks, such as limestone and gypsum, form when minerals precipitate from a solution, e.g., seawater.
Organic sedimentary rocks, like coal, form from the accumulation, compaction, and hardening of plant and animal remains.
Sedimentary rocks often have distinctive layering or bedding caused due to changes in deposition over time.

Metamorphic Rocks and Processes

Metamorphic rocks form when other rocks are subjected to heat and pressure, causing physical or chemical alteration. The original rock, or parent rock(known as the protolith), undergoes changes via different mechanisms and recrystallises.
When these rocks are subjected to pressure but not exceeded their melting point we get foliated metamorphic rocks. Rocks like slate, considered low grade, changing to schist and eventually gneiss which are high grade.
Non-foliated metamorphic rocks like marble, do not have a layered or banded appearance.
Contact metamorphism occurs when rock is heated by surrounding magma or lava.
Regional metamorphism occurs during the collision of two tectonic plates or during mountain building.

Understanding the properties and formation process of rocks and minerals is a core part of geology, enabling scientists to interpret the Earth’s dynamic history.