igneous
Diabase
Diabase (also known as Dolerite)
Hardness: 6-7 Mohs; Color: dark grey to black, often with greenish hues; Luster: vitreous to dull; Crystal structure: fine to medium-grained; Cleavage: poor; Specific gravity: approx. 3.0
- Hardness
- 6-7 Mohs
- Color
- dark grey to black, often with greenish hues
- Luster
- vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black, often with greenish hues; Luster: vitreous to dull; Crystal structure: fine to medium-grained; Cleavage: poor; Specific gravity: approx. 3.0
Formation & geological history
Formed by the rapid cooling of mafic magma in shallow intrusions such as sills and dikes. It is chemically similar to basalt and gabbro, fitting between them in grain size.
Uses & applications
Commonly used as crushed stone (trap rock) for road construction, railroad ballast, and concrete aggregate. Select specimens are used in ornamental masonry.
Geological facts
Stonehenge's inner circle 'bluestones' are partially composed of dolerite. It is significantly harder than granite, making it a difficult but durable building material.
Field identification & locations
Identify by its 'salt and pepper' appearance (tiny white plagioclase crystals against dark pyroxene) and its heavy weight. Found in major dike swarms and rift valleys globally.
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
Igneous