igneous
Basalt
Basalt (primarily Pyroxene and Plagioclase)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic when fresh; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic when fresh
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic when fresh; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most specimens belong to the Holocene or Pleistocene epochs, though it has formed throughout Earth's history.
Uses & applications
Used extensively in construction as aggregate for roads, railroad ballast, and concrete; also used for stone carving and as a heat sink in saunas.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in volcanic regions, riverbeds, and coastal areas as water-worn pebbles like the one pictured.
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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.
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