igneous
Diabase (also known as Dolerite)
Diabase / Dolerite
Hardness: 6-7 (Mohs scale); Color: Dark grey to black, often with a greenish tint; Luster: Sub-metallic to dull; Crystal structure: Phaneritic/fine-grained crystalline; Cleavage: Generally poor; Specific Gravity: 2.7–3.3
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to black, often with a greenish tint
- Luster
- Sub-metallic to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to black, often with a greenish tint; Luster: Sub-metallic to dull; Crystal structure: Phaneritic/fine-grained crystalline; Cleavage: Generally poor; Specific Gravity: 2.7–3.3
Formation & geological history
Formed from the shallow intrusion of basaltic magma into dikes or sills. It cools faster than gabbro but slower than basalt, resulting in its characteristic medium-grained texture. Most common in tectonically active areas throughout Earth's history.
Uses & applications
Primarily used as crushed stone for construction (aggregate), railroad ballast, road base, and high-durability countertops. In ancient times, it was used for monuments (e.g., portions of Stonehenge).
Geological facts
Diabase is what makes up the famous 'Palisades' along the Hudson River in NY/NJ. Many 'bluestones' used at Stonehenge are actually of a similar dolerite composition.
Field identification & locations
Identify in the field by its dark color, crystalline texture (visible under a hand lens as interlocking 'salt and pepper' grains), and extreme hardness compared to sedimentary rocks. It often weathers to a rusty brown color on the surface due to iron content.
