Diabase is a fine-to-medium-grained mafic intrusive rock that forms in shallow dikes and sills. It serves as the chemical equivalent to basalt but features a distinct sub-ophitic texture visible under a hand lens where laths of plagioclase are partially enclosed by pyroxene crystals.
Is this diabase?
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 diabase with a known reference. Diabase 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. Diabase leaves a white to gray streak.
- 3Read the lusterHold the specimen under a strong light. Diabase typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: dark gray, black, greenish-gray.
- 5Look at form & habitTypical habit: massive.
Often confused with
Diabase vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Diabase leaves white to gray, Basalt leaves white.
How to tell apart: Luster reads dull on Diabase and vitreous on Gabbro.
How to tell apart: Luster reads dull on Diabase and subvitreous to pearly on Amphibolite.
Often found alongside diabase
Minerals reported to co-occur with diabase. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6-7
- Density
- 2.8-3.1 g/cm³
- Streak
- White to Gray
- Luster
- Dull
- Transparency
- Opaque
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Construction, Road Aggregate, Decorative, Sculpture
- Host rock
- Intrusive Igneous Dikes and Sills
- Typical price
- $5-20 per specimen
Where rockhounds find diabase
1 mapped spotsClassic worldwide localities
- Palisades Sill, USA
- Scotland
- South Africa
- India
- Australia
Field-hunting tip
Look in intrusive igneous dikes and sills country, the host setting where diabase typically forms. If you start seeing plagioclase, pyroxene, magnetite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California. Start trip planning there.
Common questions
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Find diabase on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
