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Igneous rocks (scientific)

Scientific terms for igneous composition and texture: QAPF/TAS naming, grain size, and cooling history.

Nomenclature

How igneous rocks are named

Names reflect composition (silica and mineral proportions) and texture (cooling environment).

Intrusive vs. extrusive

Intrusive (plutonic) cools slowly → coarse crystals; extrusive (volcanic) cools quickly → fine crystals or glass.

Felsic to mafic

Felsic (silica-rich) vs. mafic (Mg-Fe rich). Intermediate and ultramafic fill the spectrum.

QAPF & TAS

QAPF uses modal minerals (quartz/alkali feldspar/plagioclase/feldspathoids). TAS uses chemistry for volcanic rocks.

Common scientific names

Granite, granodiorite, diorite, gabbro; rhyolite, andesite, basalt; plus obsidian, pumice, scoria, tuff.

Igneous textures

Glassy, vesicular, and crystalline textures that drive scientific descriptors.

Obsidian close-up showing volcanic glass texture Volcanic rock surface texture Granite showing coarse interlocking crystals Basalt columns showing cooling joints
Obsidian close-up showing volcanic glass texture Volcanic rock surface texture Granite showing coarse interlocking crystals Basalt columns showing cooling joints
Obsidian close-up showing volcanic glass texture Volcanic rock surface texture Granite showing coarse interlocking crystals Basalt columns showing cooling joints
Obsidian close-up showing volcanic glass texture Volcanic rock surface texture Granite showing coarse interlocking crystals Basalt columns showing cooling joints
Obsidian close-up showing volcanic glass texture Volcanic rock surface texture Granite showing coarse interlocking crystals Basalt columns showing cooling joints
Obsidian close-up showing volcanic glass texture Volcanic rock surface texture Granite showing coarse interlocking crystals Basalt columns showing cooling joints

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