Basalt

Definition

Basalt is a dark, fine-grained volcanic rock primarily composed of plagioclase and pyroxene minerals. It is the most common rock type found in the Earth's oceanic crust and on other planetary bodies like the Moon and Mars.

5 Must Know Facts For Your Next Test

1. Basalt forms from the rapid cooling of low-viscosity lava rich in iron and magnesium.
2. The ocean floors are predominantly composed of basalt, which covers over 70% of Earth's surface.
3. Lunar maria, the large dark plains on the Moon, are formed almost entirely of basaltic rock.
4. Basaltic volcanism is associated with shield volcanoes and mid-ocean ridges.
5. Martian basalts provide evidence that volcanic activity once occurred on Mars.

Review Questions

• What mineral composition characterizes basalt?
• Where on Earth can you predominantly find basalt?
• What celestial bodies besides Earth have significant amounts of basalt?

Related terms

Shield Volcano: A broad, domed volcano with gently sloping sides, characteristic of effusive eruptions producing basalt.

Mid-Ocean Ridge: An underwater mountain range formed by plate tectonics where new oceanic crust is created through volcanic activity.

Lunar Maria: Large, dark basaltic plains on the Moon's surface formed by ancient volcanic eruptions.