Igneous Rocks Lecture Notes

These flashcards cover key terms and concepts related to igneous rocks and their properties, formation, textures, and compositions.

Extrusive

Igneous rocks that form from lava on the Earth's surface.

Intrusive

Igneous rocks that form from magma cooling beneath the Earth's surface.

Felsic Magma

Light-colored magma that is high in silica and tends to be more viscous.

Intermediate Magma

Magma with a composition between felsic and mafic, containing about 25% dark silicate minerals.

Mafic Magma

Dark-colored, low-silica magma that is less viscous and often associated with oceanic crust.

Aphanitic

A fine-grained texture of igneous rocks formed by rapid cooling.

Phaneritic

A coarse-grained texture of igneous rocks formed by slow cooling.

Porphyritic

An igneous texture where large crystals are embedded in a matrix of smaller crystals.

Viscosity

A measure of a fluid's resistance to flow; in magma, it affects how easily it can erupt.

Vesicular

Texture of igneous rocks with small holes (vesicles) formed by trapped gas bubbles.

Bowen's Reaction Series

A sequence that illustrates the order in which minerals crystallize from a cooling magma.

Decompression Melting

Process where a decrease in pressure allows the melting of materials in the mantle.

Assimilation

The process of changing a magma’s composition by incorporating surrounding rock.

Magmatic Differentiation

Separation of a melt from crystallized minerals in the cooling magma.

Tuff

A volcanic rock composed of ash-sized fragments ejected during a volcanic eruption.

Obsidian

A dark volcanic glass with conchoidal fracture and no crystalline structure.

Scoria

A volcanic rock similar to basalt, often produced from cinder cone eruptions.

Partial Melting

An incomplete melting of rocks, often forming magma with a specific composition.

Pyroclastic Texture

A texture characterized by fragments produced during a violent volcanic eruption.

Pegmatitic Texture

An exceptionally coarse-grained texture typically formed in the late stages of crystallization.

Viscous

Thick and sticky; a property of magma that affects its flow and eruption.