igneous
Diabase (Greenstone)
Diabase (also known as Dolerite)
Hardness: 6-7 on Mohs scale; Color: Dark grey to greenish-black; Luster: Sub-vitreous to dull; Crystal structure: Fine to medium-grained phaneritic (ophitic texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.7–3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to greenish-black
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to greenish-black; Luster: Sub-vitreous to dull; Crystal structure: Fine to medium-grained phaneritic (ophitic texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.7–3.3.
Formation & geological history
Formed from the shallow cooling of mafic magma in intrusive bodies like sills and dikes. Historically associated with the Triassic-Jurassic period (approx. 200 million years ago) in areas like the Central Atlantic Magmatic Province.
Uses & applications
Used primarily as crushed stone for construction (road base, railroad ballast) and 'black granite' for monuments. Some varieties are polished for ornamental use.
Geological facts
Stonehenge's inner 'bluestones' are made of a type of diabase. It is chemically equivalent to basalt but has larger crystals due to slower cooling underground.
Field identification & locations
Identify in the field by its distinctive 'salt and pepper' appearance under a hand lens and its heavy weight for its size. Common in the Appalachian mountains (USA), UK, and South Africa. Collectors should look for weathered surfaces which often turn brown.
