igneous
Basalt
Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.9-3.1
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.9-3.1
Formation & geological history
Basalt is an extrusive igneous rock 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. It predominantly forms at mid-ocean ridges and hotspots.
Uses & applications
Extensively used in construction for road base, concrete aggregate, and railroad ballast. It is also used as dimension stone for flooring and as a primary material in the production of rock wool insulation.
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, Mars, and Venus, where large volcanic flows have been observed.
Field identification & locations
Identify by its dark color, heavy weight compared to other similar-looking rocks, and lack of visible crystals. It is commonly found in volcanic regions and ocean floor outcroppings. Look for vesicular (pitted) or massive textures.
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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