igneous
Diabase (Dolerite)
Diabase or Dolerite
Hardness: 6-7 on Mohs scale. Color: Dark grey to black with white speckling. Luster: Dull (sub-vitreous on fresh surfaces). Crystal Structure: Fine to medium-grained phaneritic, often showing an ophitic texture where laths of plagioclase are enclosed in pyroxene. Specific Gravity: 2.7 - 3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black with white speckling
- Luster
- Dull (sub-vitreous on fresh surfaces)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to black with white speckling. Luster: Dull (sub-vitreous on fresh surfaces). Crystal Structure: Fine to medium-grained phaneritic, often showing an ophitic texture where laths of plagioclase are enclosed in pyroxene. Specific Gravity: 2.7 - 3.3.
Formation & geological history
Formed through the rapid cooling of mafic magma (similar to basalt) injected into shallow dikes or sills within the Earth's crust. It is typically Mesozoic or older in many well-known formations, like the Palisades Sill.
Uses & applications
Extensively used as crushed stone (trap rock) for road construction, railroad ballast, and concrete aggregate. High-quality slabs are sometimes used as building stone or as a base for precision instruments due to thermal stability.
Geological facts
It is the intrusive equivalent of basalt and the extrusive equivalent of gabbro. The famous Stonehenge inner circle consists of 'Bluestone,' which is a type of dolerite.
Field identification & locations
Identify in the field by its high density, dark color, and 'salt and pepper' appearance of tiny crystals. It is commonly found in rift basins and volcanic provinces worldwide, often forming prominent ridges due to its resistance to erosion.
