basalt
n. uncountablen. a dark, heavy rock that comes from cooled lava. It is the most common type of rock found on the ocean floor and in many volcanic areas.
n. a dark-coloured, fine-grained igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava. It is the primary constituent of the oceanic crust and common in volcanic provinces.
The cliffs along the coast are made of dark basalt.
Geologists identified the formation as basalt, noting the characteristic hexagonal columns created as the lava cooled and contracted.
The island's rugged interior is dominated by vast basalt plateaus, evidence of ancient volcanic activity that reshaped the landscape millions of years ago.
From Late Latin basaltes, a misspelling of Latin basanites, from Ancient Greek βασανίτης (basanítēs), from βάσανος (básanos, “touchstone”), from Egyptian bḫn (“a hard stone”), b-x:n-O39
Used uncountably for the material; can be countable when referring to specific geological types or formations.