The Rock Cycle

Study Notes

A rock is a naturally occurring solid cohesive aggregate of one or more mineral or mineral materials.
Rocks are broadly classified into three groups based on their process of formation: igneous, sedimentary, and metamorphic rocks.

Sedimentary rocks make up 66% of the earth's crust, with 34% being igneous and metamorphic.
Sedimentary rocks are mainly found on ocean floor basins, which account for 70% of the total area of the earth.

Igneous rocks are formed from the solidification and cooling of magma, which can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust.
The melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.
Igneous rocks are divided into two main categories: plutonic (intrusive) and volcanic (extrusive).
Plutonic rocks result when magma cools and crystallizes slowly within the Earth's crust, forming rocks such as granite.
Volcanic rocks result from magma reaching the surface, forming rocks such as pumice or basalt.
The chemical abundance and the rate of cooling of magma typically form a sequence known as Bowen's reaction series.

The texture of an igneous rock is determined by the temperature of the cooling magma.
Igneous rocks can be differentiated according to their texture, color, and composition depending on the environment of deposition and the chemistry of magmas.
The color of igneous rocks is determined by its dominant minerals, with dark minerals forming mafic rocks and lighter minerals forming felsic rocks.
Magma chemistry is determined by its Silica content, with rocks classified as mafic, felsic, or ultra-mafic based on their silica content.

Metamorphic rocks are rocks that have experienced change due to high pressure and temperature below the zone of diagenesis.
The original rock, prior to metamorphism, is referred to as the protolith.
In low-grade metamorphic rocks, original textures are often preserved, allowing one to determine the likely protolith.