Types of Rocks

Study Notes

Rocks are defined as naturally occurring aggregates of geological material, called minerals.
The three major types of rocks are igneous rocks, sedimentary rocks, and metamorphic rocks.

Igneous rocks are formed from the cooling and solidification of molten rock (magma).
Magma can cool and solidify beneath the Earth's crust or on the surface, resulting in two types of igneous rocks:
- Intrusive igneous rocks: solidify within the Earth's crust, characterized by large, visible crystal formations.
- Extrusive igneous rocks: formed by the cooling and solidification of lava on the Earth's surface, characterized by rapid cooling and small, invisible crystal structures.

Sedimentary rocks are defined as lithified sediments.
Sediments can come from:
- Weathering of rocks due to forces like wind and water.
- Dead organic matter.
- Precipitated salts.
Accumulated sediments can become lithified (turned into rock) due to compaction, cementing, or other processes.

Clastic sedimentary rocks: formed by the lithification of sediments called clasts, produced by the weathering of other rocks.
Organic sedimentary rocks: formed by the lithification of sediments from organic materials, such as bones, shells, and teeth.
Chemical sedimentary rocks: formed when water evaporates and produces sediments of dissolved matter.

Metamorphic rocks are formed through the metamorphosis of sedimentary or igneous rocks.
Metamorphosis is the change in rock type due to environmental factors like heat, pressure, or chemical environments.

Foliated metamorphic rocks: characterized by the presence of parallel bands of minerals running through the rock.
Unfoliated metamorphic rocks: formed when pressure is milder across the rock during the process of metamorphosis.

Contact metamorphism: occurs when magma rises to the upper crust of the Earth, generating high heat and low pressure conditions.
Regional metamorphism: occurs at convergent tectonic margins, where two continental plates collide, generating high heat and pressure conditions.
Dynamic metamorphism: occurs as a result of mechanical deformation, often seen along fault lines.

The rock cycle describes how geological material, such as rocks and minerals, are cycled over time.
It considers the relation between igneous, sedimentary, and metamorphic rocks and how transformations occur between each type.
The rock cycle is a continuous process where rocks can change from one type to another due to various environmental factors.