Rocksday

Basalt

The most common volcanic rock on Earth. Dark, fine-grained lava that forms the ocean floor and vast lava plains.

Basalt specimen
Photo: James St. John, CC BY 2.0, via Wikimedia Commons

How to identify basalt

  • Dark gray to black and heavy.
  • Grains too small to see.
  • Often has gas bubbles (vesicles).
  • May show six-sided columns in outcrops.

Often confused with

Where it's found

  • Hawaii
  • Iceland
  • Columbia River Plateau
  • Giant's Causeway, Northern Ireland

Uses

Road aggregate, rock-wool insulation and basalt fiber.

Rock tumbling

Can be tumbled with care.

Did you know?

The dark 'seas' you see on the Moon are giant plains of basalt.

Think you could spot it from a blurry close-up?

Play today's Rocksday