Gabbro is a dark-colored, coarse-grained intrusive igneous rock composed primarily of plagioclase feldspar and pyroxene. It is the plutonic equivalent of basalt and is often found in large, deep-seated igneous bodies. Collectors frequently seek it for its structural textures and as a source for accessory minerals like magnetite or chromite.
Is this gabbro?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch gabbro with a known reference. Gabbro sits at Mohs 6-7, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Texture: Phaneritic and holocrystalline. Grain size: Coarse-grained.
- 3Pick out the mineralsComposition: Mostly clinopyroxene and calcium-rich plagioclase, with minor hornblende, olivine and orthopyroxene. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 5Match the color rangeCompare against the expected color range: black, dark green, dark gray.
Often confused with
Gabbro vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside gabbro
Minerals reported to co-occur with gabbro. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6-7
- Density
- 2.7-3.3 g/cm³
- Colors
- Luster
- Vitreous
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Building stone, Decorative, Industrial
- Host rock
- plutonic environments
- Texture
- Phaneritic and holocrystalline
- Grain size
- Coarse-grained
- Composition
- Mostly clinopyroxene and calcium-rich plagioclase, with minor hornblende, olivine and orthopyroxene
Where rockhounds find gabbro
Classic worldwide localities
- Bushveld Complex, South Africa
- Stillwater Complex, USA
- Duluth Complex, USA
- Skye, Scotland
- Norway
Field-hunting tip
Where it forms: plutonic environments. If you start seeing plagioclase, pyroxene, olivine in float, you are in the right ground.
Common questions
How do you identify gabbro?+
Where is gabbro found?+
What rocks look like gabbro?+
What minerals are found with gabbro?+
What kind of rock does gabbro form in?+
What is gabbro used for?+
Find gabbro on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
