Rock Formation: Metamorphic, Sedimentary, and Igneous Rocks

Study Notes

Metamorphic rocks are formed from pre-existing rocks (igneous, sedimentary, or other metamorphic rocks) under high pressure, high temperature, and/or chemically active fluids.
This process, called metamorphism, occurs deep within the Earth's crust.
Examples of metamorphic rocks include slate (from shale), marble (from limestone), and schist (from various precursor rocks).
Metamorphic rocks often have a foliated or banded texture due to the reorientation of minerals under pressure.
They can also be non-foliated if they form under conditions where deformation is minimal.

Sedimentary rocks form from the accumulation and lithification of sediments, which are particles of rock, minerals, and organic material.
These sediments are typically deposited in layers by water, wind, or ice.
Examples of sedimentary rocks include sandstone (from sand), limestone (from calcite or organic material), and shale (from clay or mud).
Sedimentary rocks often have a layered appearance (strata) and may contain fossils.
They can be clastic (formed from fragments of other rocks), chemical (precipitated from solutions), or organic (composed of organic material).

Igneous rocks form from the cooling and solidification of molten rock material called magma (below the surface) or lava (at the surface).
This process can occur either beneath the Earth's surface (intrusive) or at the surface (extrusive).
Examples of igneous rocks include granite (intrusive) and basalt (extrusive).
Igneous rocks are classified based on their texture (grain size) and mineral composition.
Intrusive igneous rocks have coarse-grained textures due to slow cooling, while extrusive igneous rocks have fine-grained or glassy textures due to rapid cooling.

Igneous rocks originate from molten material, sedimentary rocks from the deposition of sediments, and metamorphic rocks from the transformation of existing rocks.
Igneous rocks form in volcanic and plutonic environments, sedimentary rocks in surface environments (rivers, lakes, oceans), and metamorphic rocks in deep crustal regions with high pressure and temperature.
Igneous rocks have crystalline textures, sedimentary rocks typically have layered textures, and metamorphic rocks often exhibit foliation or banding.

The formation processes are distinct: cooling and solidification for igneous rocks, deposition and lithification for sedimentary rocks, and heat and pressure for metamorphic rocks.
Sedimentary rocks can form relatively quickly from deposited sediments, igneous rocks can solidify in a range of times from quickly (extrusive) to slowly (intrusive), and metamorphic rocks generally form over longer geological timescales.
Metamorphic rocks undergo significant mineralogical changes due to metamorphism, while sedimentary rocks primarily involve the physical deposition of material, and igneous rocks crystallize from a melt.