Diabase
Diabase is a dark, medium-grained mafic igneous rock, also called dolerite in many regions. It commonly forms in dikes and sills and sits texturally between basalt and gabbro.
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Diabase properties at a glance
| Type | Igneous Rocks |
|---|---|
| Chemical formula | Variable mineral composition |
| Mohs hardness | 6 |
| Luster | varies |
| Streak | Variable; test individual minerals |
| Cleavage | Variable by mineral grains |
| Fracture | Uneven to granular |
| Specific gravity | 2.8 |
| Transparency | opaque |
| Common colors | Various |
| Rarity | common |
Geology & background
Forms from molten rock as magma or lava cools and crystallizes.
Diabase helps geologists interpret the environment and processes that formed a landscape.
How to identify Diabase
- Look for dark, dense, medium-grained igneous texture.
- Diabase is also commonly called dolerite outside North America.
- It is usually coarser than basalt and finer than gabbro.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Diabase is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Diabase worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Field identification
- Construction or aggregate when suitable
- Landscape interpretation
- Education
Interesting facts
- Diabase is useful for field identification because texture, color, luster, and context can narrow the match.
- Specimens labeled Diabase can vary by locality, weathering, impurities, and crystal or grain size.
- A fresh surface and multiple photos usually improve identification confidence.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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