Rocksday

Gabbro

A dark, coarse-grained rock made of pyroxene and plagioclase — basalt that cooled slowly underground.

Gabbro specimen
Photo: Darla Sondrol, CC0, via Wikimedia Commons

How to identify gabbro

  • Dark gray to black with visible crystals.
  • Heavy.
  • Little or no quartz.
  • Gray plagioclase may show faint parallel lines.

Often confused with

Where it's found

  • Duluth Complex, Minnesota
  • Cuillin, Isle of Skye
  • Bushveld, South Africa
  • Ocean crust

Uses

Countertops, monuments and crushed stone.

Rock tumbling

Great for tumbling.

Did you know?

Much of what is sold as 'black granite' is actually gabbro.

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

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