igneous
Basalt
Basaltic Mafic Rock
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte, Crystal structure: Fine-grained/Aphanitic, Specific Gravity: 2.8 - 3.0, Cleavage: None
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte, Crystal structure: Fine-grained/Aphanitic, Specific Gravity: 2.8 - 3.0, Cleavage: None
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found in oceanic crust, mid-ocean ridges, and volcanic hotspot regions.
Uses & applications
Used extensively in construction as road base, concrete aggregate, railroad ballast, and for stone masonry. Sometimes used for statues and pavement.
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, Mars, and Venus.
Field identification & locations
Identify by its dark charcoal color and very small, barely visible crystals. Found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest. Heavy and dense compared to lighter-colored igneous rocks.
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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