igneous
Diabase (Trap Rock)
Diabase (also known as Dolerite)
Hardness: 6-7 on Mohs scale; Color: Dark gray, green-black to black; Luster: Dull to sub-vitreous; Crystal structure: Fine to medium-grained (interlocking plagioclase and pyroxene); Specific gravity: 2.7-3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark gray, green-black to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark gray, green-black to black; Luster: Dull to sub-vitreous; Crystal structure: Fine to medium-grained (interlocking plagioclase and pyroxene); Specific gravity: 2.7-3.3.
Formation & geological history
Formed from the shallow cooling of mafic magma in dikes and sills. These are intrusive rocks that cool faster than gabbro but slower than basalt. Often associated with volcanic activity and continental rifting during the Mesozoic Era.
Uses & applications
Extensively used as crushed stone for construction, road base (railroad ballast), and as ornamental stone for building facades or memorials. It is extremely durable and weather-resistant.
Geological facts
The famous Palisades Sill along the Hudson River is primarily composed of diabase. Some Stonehenge stones (called 'bluestones') are actually varieties of diabase/dolerite transported from Wales.
Field identification & locations
Identify by its 'salt and pepper' or dark greenish appearance with a lack of visible quartz. In the field, look for characteristic columnar jointing or blocky fracturing. Common in the Triassic-Jurassic basins of the Eastern US and Europe.
