Diabase (also called dolerite) is a hard, fine-grained basic igneous rock with a composition similar to basalt and gabbro, but sitting between them in cooling rate and grain size. It is one of the most sought-after natural stones for heavy civil-engineering applications.
Origin and composition
Diabase forms where magma cools relatively quickly underground in cracks and fissures within existing rocks. Cooling is faster than for gabbro (so the grains stay finer) but slower than for basalt (so they are coarser and more crystalline). The main minerals are:
- Plagioclase (calcium-rich feldspar) — about 40–60 %
- Pyroxene (mainly augite) — about 30–50 %
- Olivine and ore minerals — in smaller amounts
Because of these dark minerals, diabase is usually dark grey to black.
Properties
Diabase is valued for:
- High compressive strength — up to 300 N/mm² (many times that of concrete)
- Excellent wear resistance — Mohs hardness 6–7
- Low water absorption — below 0.5 %
- Frost resistance — outstanding, even under many freeze-thaw cycles
- High density — around 2,950 kg/m³
- Good splitting behaviour — breaks readily into block shap
The main technical properties that make diabase suitable for heavy infrastructure. es
Applications
Because of these properties, diabase is used mainly in heavy infrastructure:
| Use | Reason |
|---|---|
| Railway ballast | Wear resistant, dense enough to stabilise track |
| Asphalt for heavily trafficked roads | High wear resistance and skid resistance |
| High-strength concrete (marine works) | High strength and density |
| Bank protection and rip-rap | Frost- and flow-resistant |
| Pavers and kerbs | Skid-resistant and decorative |
| Gabions | Coarsely broken diabase |
Sources
Many countries lack workable diabase reserves and import the material from regions such as:
- Germany (Sauerland, Eifel, Lusatia)
- Belgium (Wallonia)
- Scandinavia (Norway and Sweden)
- Scotland
At the quarry the stone is crushed into various size fractions (e.g. 2–5 mm, 8–16 mm, 32–63 mm) and shipped by sea or rail to the user.
How diabase differs from basalt and gabbro
| Rock | Cooling | Grain size |
|---|---|---|
| Basalt | Fast (at surface) | Very fine |
| Diabase | Intermediate (in fissures) | Fine to medium |
| Gabbro | Slow (deep in crust) | Coarse |
Chemically all three are closely related: basic (silica-poor), dark and dense.
Related terms
- Natural stone
- Basalt
- Aggregate
- Asphalt
- Rubble stone
- Gabion
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