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.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Gabbro leaves a none streak.
- 3Read the lusterHold the specimen under a strong light. Gabbro typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark green, dark gray.
- 5Look at form & habitTypical habit: granular.
Often confused with
Gabbro vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Gabbro leaves none, Diorite leaves white.
How to tell apart: Streak differs — Gabbro leaves none, Peridotite leaves white; luster reads vitreous on Gabbro and vitreous to dull on Peridotite.
How to tell apart: Streak differs — Gabbro leaves none, Basalt leaves white; luster reads vitreous on Gabbro and dull on Basalt.
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
- Streak
- None
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal habit
- Granular
- Cleavage
- None
- Rarity
- Common
- Uses
- Building Stone, Decorative, Industrial
- Host rock
- Plutonic Environments
- Typical price
- $5-30 for slabs or architectural samples
Where rockhounds find gabbro
Classic worldwide localities
- Bushveld Complex, South Africa
- Stillwater Complex, USA
- Duluth Complex, USA
- Skye, Scotland
- Norway
Field-hunting tip
Look in plutonic environments country — that is the host setting where gabbro typically forms. If you start seeing plagioclase, pyroxene, olivine in float, you are in the right ground. Field specimens usually show a granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gabbro on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
