igneous
Diabase (also known as Dolerite)
Diabase
Hardness: 6-7 on Mohs scale. Color: Dark gray to black, often with greenish hues or white speckling from feldspar. Luster: Sub-vitreous to dull. Crystal structure: Fine to medium-grained ophitic texture. Specific gravity: 2.7-3.3.
- Hardness
- 6-7 on Mohs scale
- Luster
- Sub-vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark gray to black, often with greenish hues or white speckling from feldspar. Luster: Sub-vitreous to dull. Crystal structure: Fine to medium-grained ophitic texture. Specific gravity: 2.7-3.3.
Formation & geological history
Formed through the cooling of mafic magma in shallow intrusive bodies like dikes and sills. It is chemically similar to basalt but has a coarser grain size due to slower cooling underground.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and building foundations. High-quality specimens are sometimes used as 'black granite' in monuments and countertops.
Geological facts
Diabase is famous for its role in the construction of Stonehenge; the 'bluestones' used in the inner circle are a type of spotted dolerite. It is also the primary rock type of the Palisades sill along the Hudson River.
Field identification & locations
Identify it by its heavy weight, dark color, and interlocking grain texture. It won't scratch with a steel nail. Commonly found in areas of rifting or volcanic activity, such as the Appalachian Mountains or the Karoo Basin.
