igneous
Basalt (River Stone)
Basalt (Extrusive Igneous Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal or black (sometimes greenish if weathered); Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on Mohs scale
- Luster
- Dull or earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal or black (sometimes greenish if weathered); Luster: Dull or earthy; 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 at or very near the Earth's surface. This particular specimen shows rounding due to water erosion, suggesting it was sourced from a riverbed or coastal environment.
Uses & applications
Basalt is used extensively in construction as aggregate for concrete and asphalt, as railroad ballast, and sometimes in polished form for floor tiles or jewelry.
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 common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight compared to its size, and absence of visible large crystals. Most common in volcanic regions or as smooth pebbles in ancient riverbeds.
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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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