igneous
Diabase (Greenstone Pebble)
Diabase or Dolerite
Hardness: 6-7 on Mohs scale; Color: Grayish-green or dark teal; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic/Fine-to-medium grained equigranular; Cleavage: Poor; Specific gravity: 2.7–3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Grayish-green or dark teal
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Grayish-green or dark teal; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic/Fine-to-medium grained equigranular; Cleavage: Poor; Specific gravity: 2.7–3.3.
Formation & geological history
Formed through the cooling of mafic magma in shallow intrusive bodies like dikes or sills. This specific specimen has been Rounded and smoothed by 'alluvial' or 'littoral' action (water erosion) over thousands of years.
Uses & applications
Used primarily as crushed stone for road construction, railroad ballast, and high-strength concrete. When polished as 'greenstone' pebbles, they are common in landscaping and aquarium decor.
Geological facts
Greenish hues in these pebbles often come from the alteration of pyroxene minerals into chlorite, epidote, or actinolite. The most famous use of diabase is 'Bluestone' used in the inner circle of Stonehenge.
Field identification & locations
Look for a heavy, dense feel for its size and a 'salt and pepper' appearance of dark and light minerals under a magnifying glass. Commonly found on beaches and riverbeds in volcanic regions.
