What does basalt mean?
Basalt is a dark, fine-grained igneous rock that forms when lava cools rapidly at or near the Earth's surface, giving its minerals too little time to grow into large crystals. It is typically grey to black, dense, and hard, and it makes up most of the ocean floor as well as enormous lava plateaus on land, such as those in Iceland and northwestern India. Because it is abundant and durable, basalt has long been used for building, road aggregate, and sculpture — famous columnar formations like the Giant's Causeway in Northern Ireland showcase its striking natural geometry. In everyday English the word is a mass noun, appearing mainly in geological, geographical, and industrial contexts. For readers, basalt is worth knowing both as the planet's most common volcanic rock and as a word that evokes dramatic volcanic scenery and ancient stone architecture.
nounA dark, fine-grained igneous rock formed from the rapid cooling of lava at or near the Earth's surface; it is the most abundant rock in the oceanic crust.
- A dark, fine-grained igneous rock formed from rapidly cooled lava, the chief constituent of the ocean floor and of extensive lava plateaus.
"The cliffs of the Giant's Causeway are formed of hexagonal columns of basalt."
"Iceland's landscape is dominated by vast fields of black basalt laid down by ancient eruptions."
"Crushed basalt is widely used as aggregate in road construction because of its hardness and durability."
Rare outside specialist geological writing, where different varieties of basalt are distinguished; in ordinary usage basalt is treated as a mass noun.
"The region contains several chemically distinct basalts erupted over millions of years."
The Giant's Causeway in Northern Ireland is built from roughly 40,000 interlocking basalt columns — nature's own pavement, poured by lava some 60 million years ago.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of basalt
The word basalt entered English in the early 17th century, borrowed from Latin basaltes, which itself derived from Greek basanites, meaning a touchstone-like dark stone. The ultimate origin is often traced to Egyptian bauhun or a related source via Greek, though the precise chain of transmission is uncertain. The adjective form basaltic developed later to describe rocks and lavas composed of or resembling basalt.
Related word forms
How basalt is actually used
Basalt is a technical term used chiefly in geology, but it also appears in general writing about landscapes, monuments, and construction. It is always a mass noun in ordinary use; the plural 'basalts' appears only in specialist geological literature to distinguish varieties of the rock.
Easily confused with basalt
Granite is a coarse-grained, light-colored intrusive igneous rock that cooled slowly underground, whereas basalt is fine-grained, dark, and formed from rapidly cooled surface lava.
Obsidian is volcanic glass with no crystalline structure, while basalt is a crystalline rock made of tiny mineral grains.