What does andesite mean?
Andesite is a fine-grained volcanic rock of intermediate chemical composition, made up predominantly of plagioclase feldspar together with dark minerals such as pyroxene or amphibole. It forms when magma with a moderate silica content erupts at the surface and cools quickly, producing a dense grey to dark-grey stone. Named after the Andes mountains, where it was first formally described, andesite is especially characteristic of the chains of steep stratovolcanoes that rise above subduction zones, including the Andes themselves, the Cascades of the Pacific Northwest, and the island arcs of the Pacific. Its viscous lava tends to trap gases, which helps explain why andesitic volcanoes are prone to explosive eruptions. Beyond geology, andesite has practical value as a hard-wearing building and road stone, and it was prized by ancient Andean civilisations for sculpture and construction. The adjective form is andesitic, used to describe lavas and magmas of this composition.
nounA fine-grained, usually grey volcanic rock of intermediate composition, consisting chiefly of plagioclase feldspar along with pyroxene or amphibole. It is the most common lava erupted by stratovolcanoes above subduction zones.
- A fine-grained extrusive igneous rock of intermediate composition, composed mainly of plagioclase feldspar with ferromagnesian minerals such as pyroxene or amphibole.
"The towering volcanoes of the Cascades are built largely of andesite, erupted as thick, slow-moving lava flows."
"Geologists identified the summit dome as andesite, confirming the volcano's explosive potential."
"Ancient builders in the Andes quarried durable andesite for walls and monuments that still stand today."
Rarely pluralised; the plural appears only when referring to distinct varieties or occurrences of the rock, e.g. in petrographic classification.
"The map distinguishes two chemically distinct andesites within the same volcanic complex."
Andesite takes its name from the Andes mountains, where it was first systematically described — the rock that builds some of the world's most explosive volcanoes literally borrowed the name of the range it forms.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of andesite
The word andesite derives from the Andes, the South American mountain range where the rock was first systematically studied and described by geologists in the nineteenth century. It belongs to a family of rock names modelled on geographic type localities, alongside minerals such as andesine, a plagioclase feldspar also named for the Andes. The suffix -ite follows the standard convention for naming rocks and minerals in English scientific nomenclature.
Related word forms
How andesite is actually used
Andesite is a technical term used mainly in geology, volcanology, and earth-science education; it carries no figurative or informal usage. It is always written as a mass noun for the rock type rather than counted in discrete units.
Easily confused with andesite
Basalt is a mafic volcanic rock richer in iron and magnesium and darker in colour, whereas andesite is intermediate in composition and typically lighter grey.
Rhyolite is a felsic volcanic rock rich in silica and quartz, while andesite has an intermediate silica content and little or no quartz.
Dacite is closely related to andesite but contains more silica and noticeable quartz, placing it between andesite and rhyolite.