rhizoverbBeta
DictionarybasaltVolcanic rock
noun

basalt

buh-SAWLT/bəˈsɔːlt/

A dark, fine-grained volcanic rock.

Dark basalt columns rise above a broken fine-grained fragment.

A compact basalt outcrop with dark, tightly fitted polygonal columns and a broken fine-grained chunk in the foreground; a small cooling lava flow behind it establishes its volcanic origin.
Etymology
basaltLatinvery hard stone

The “very hard stone” behind this name was a gold-testing touchstone: assayers compared streaks left by genuine gold and suspect metal. The name came to denote dark volcanic rock rather than its testing use.

In context

LifesBiggestQuestions67:15
molten Basalt cooled and contracted to form the hexagonal columns championed by James Hutton in the late 18th century
3 Hours Of Ancient Megalithic Structures That Humans Could Not Have Built

More examples

  • Columns of basalt rose along the cliff.
  • The sample had the fine grain typical of basalt.
  • The path crossed an old basalt flow.

Forms

basalt

Similar words

granite
Granite is generally coarse-grained and forms underground; basalt is fine-grained volcanic rock.
obsidian
Obsidian is volcanic glass; basalt is a crystalline volcanic rock.