Igneous Rocks and Temperature – Vocabulary Flashcards

Vocabulary flashcards covering key igneous rock concepts from the notes.

Extrusive igneous rocks

Rocks formed on the surface when magma erupts as lava and cools rapidly, producing a fine-grained or glassy texture.

Intrusive igneous rocks

Rocks formed below the surface when magma crystallizes slowly at depth, producing a coarse-grained texture.

Lava

Molten rock that erupts onto the surface.

Pyroclasts

Rock fragments ejected during explosive volcanic eruptions; can include ash, bombs, and pumice.

Country rock

Preexisting rock that is present before an intrusion and may be assimilated or broken up by invading magma.

Xenolith

A fragment of country rock or mantle rock incorporated into an intrusive or extrusive rock.

Texture

The visual grain size and arrangement of minerals in a rock.

Aphanitic

Fine-grained texture where crystals are too small to see with the naked eye.

Phaneritic

Coarse-grained texture with crystals large enough to be seen without a microscope.

Silica content

The percentage of silicon dioxide (SiO2) used to classify igneous rocks as felsic, intermediate, mafic, or ultramafic.

Felsic

Rocks with high silica content and light-colored minerals like quartz and feldspar.

Intermediate

Rocks with moderate silica content between felsic and mafic.

Mafic

Rocks with lower silica content and higher magnesium and iron; typically darker in color.

Ultramafic

Rocks with very low silica and high magnesium-iron content, often mantle-derived.

Bowen's reaction series

A sequence describing orderly mineral crystallization as magma cools, e.g., olivine → pyroxene → amphibole → biotite → feldspar → quartz.

Fractional crystallization

Process where early-formed crystals settle out of the melt, changing the composition of the remaining magma.

Silicate tetrahedra

SiO4 units that link to form silicate minerals; their polymerization leads to isolated tetrahedra, single chains, double chains, sheets, and three-dimensional frameworks.

Volatiles

Gases dissolved in magma, especially water (H2O) and carbon dioxide (CO2), affecting melting, eruption, and atmospheric chemistry.

Mantle peridotite

An ultramafic mantle rock rich in olivine and pyroxene; representative of the upper mantle.

Basalt

A mafic extrusive rock that forms from rapid cooling at the surface; low silica compared with felsic rocks.

Gabbro

A mafic intrusive rock, the coarse-grained counterpart to basalt.

Granite

A felsic intrusive rock with high silica and light-colored minerals; coarse-grained.

Diorite

An intermediate intrusive rock with a mix of felsic and mafic minerals.

Andesite

An intermediate extrusive rock.

Rhyolite

A felsic extrusive rock with a fine-grained texture.

Komatiite

A very mafic ultramafic extrusive rock, typically mantle-derived and high in magnesium; rare in the present day.

Olivine

First mineral to crystallize in Bowen's series; ultramafic and magnesium-rich.

Pyroxene

Early-crystallizing silicate mineral in mafic magmas.

Amphibole

Silicate mineral that crystallizes after pyroxene; common in intermediate to felsic rocks.

Biotite

A mica that appears in later stages of crystallization.

Feldspar

Group of silicate minerals (plagioclase and K-feldspar) that crystallize in later stages and are major rock-forming minerals.

Quartz

Silica (SiO2) mineral; crystallizes late in Bowen’s sequence and is characteristic of felsic rocks.

Magma

Hot, molten rock stored below the surface; melts at depth and may rise as lava when erupted.

Melt vs solid rock

Melt is molten rock; solid rock is unmelted, though both can coexist during partial melting.

Crystallization temperature

Temperature at which minerals begin to crystallize from a cooling magma.

Buoyancy

Tendency of magma to rise through the crust because it is less dense than surrounding rock; rate depends on viscosity.

Viscosity

Resistance to flow in magma; higher with higher silica content and lower temperatures; affects magma ascent.

Assimilation

Process by which magma melts and incorporates surrounding country rock during intrusion.

Mixing

Magma from different sources inter mingle and combine to form a new magma composition.

Magma generation conditions

Magma forms via decreasing pressure (decompression melting), increasing temperature, or addition of volatiles (H2O, CO2) to rocks.