Lecture 7: Igneous Rocks

Vocabulary flashcards covering igneous rocks concepts from Lecture 7.

Magma

Molten rock originating below the surface that crystallizes to form igneous rocks; produced at divergent boundaries, subduction zones, and hot spots.

Lava

Magma that erupts onto the surface and cools to form volcanic rocks.

Interlocking texture

A rock texture where mineral grains fit together tightly with no gaps as they crystallize.

Aphanitic

Fine-grained texture with crystals too small to see with the naked eye, typically from rapid cooling.

Phaneritic

Coarse-grained texture with crystals visible to the naked eye, typically from slow cooling.

Porphyritic texture

A texture with large crystals (phenocrysts) embedded in a finer groundmass, formed by two-stage cooling.

Intrusive (Plutonic)

Igneous rocks that crystallize below the surface, usually coarse-grained.

Extrusive (Volcanic)

Igneous rocks that crystallize at the surface, typically fine-grained or glassy.

Mafic

Composition rich in iron and magnesium with darker minerals; lower silica; examples basalt and gabbro.

Felsic

Composition high in silica and light-colored minerals (quartz, feldspars); generally light-colored rocks like granite and rhyolite.

Intermediate

Composition between felsic and mafic; examples diorite and andesite.

Silicate minerals

Primary minerals in igneous rocks (e.g., quartz, feldspars, micas, pyroxene, amphibole, olivine); crystallization depends on magma composition and temperature.

Olivine

Dark-green silicate mineral rich in magnesium and iron; common in mafic and ultramafic rocks.

Quartz

SiO2 mineral that is a key light-colored component in felsic rocks; crystallizes from silica-rich magmas.

Vesicles

Gas-filled cavities in volcanic rocks formed when dissolved volatiles exsolve as lava reaches the surface.