Igneous Rocks Overview

Study Notes

Igneous rocks form from the cooling and hardening of molten magma.
Magma is molten rock found beneath the Earth's surface.
Lava is molten rock that has erupted onto the Earth's surface.
Intrusive igneous rocks form when magma cools slowly beneath the surface, resulting in larger crystals.
Extrusive igneous rocks form when lava cools rapidly at the surface, resulting in smaller crystals.
The rate of cooling affects the size of the crystals in the rock.
Intrusive rocks have a coarse texture and are called phaneritic.
Extrusive rocks have a fine texture and are called aphanitic.
Vesicular rocks have a porous texture due to trapped gas bubbles when lava cools rapidly.
The composition of igneous rocks can be classified by their silica content:
- Mafic rocks are dark in color and contain more magnesium and iron.
- Felsic rocks are light in color and contain more potassium, aluminum, and sodium.
- Intermediate rocks fall between mafic and felsic.

Sedimentary rocks form from the compaction and cementation of sediments.
Sediments are fragments of rock that have been broken down by weathering.
Weathering is the process of breaking down rocks, soil, and minerals through physical or chemical processes.
Erosion is the process of moving sediments by wind, water, or ice.
Deposition is the process of sediments accumulating in a new location.
Compaction is the process of sediments being pressed together by the weight of overlying layers.
Cementation is the process of new minerals filling the spaces between sediments, binding them together.
Sedimentary rocks are characterized by a layered or stratified structure called strata.
Strata often contain valuable information about the Earth's past environment.
Sedimentary rocks often contain visible particles or fragments of various sizes that are sorted by size during deposition.
Sedimentary rocks exhibit a varied composition, including mineral grains, organic matter, and chemical precipitates.

Metamorphic rocks form from the transformation of existing rocks under high pressure and temperature.
The original rocks are called the "parent rock".
Metamorphism can occur through the process of regional metamorphism or contact metamorphism.
Regional metamorphism occurs over a large area due to tectonic plate compression.
Contact metamorphism occurs when rocks are heated by contact with molten magma.
Metamorphic rocks typically exhibit foliation, a layered structure that results from the alignment of minerals under pressure.
Examples of metamorphic rocks include slate, marble, and gneiss.

The rock cycle is a continuous process of the Earth's rocks being transformed into different types.
Igneous rocks can be weathered and eroded to form sediments.
Sediments can be compacted and cemented into sedimentary rocks.
Existing rocks can be subjected to high pressure and temperature to form metamorphic rocks.
Metamorphic rocks can be melted and recrystallized to form igneous rocks.
The rock cycle is a dynamic and ongoing process that shapes the Earth's crust.

Minerals are naturally occurring, inorganic solids with a defined chemical composition and crystalline structure.
Minerals are the building blocks of rocks.
They have specific physical properties, such as hardness, cleavage, streak, luster, color, and crystal shape.
Common minerals include quartz, feldspar, mica, calcite, and halite.

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