igneous
Basalt
Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 6 (Mohs), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8-3.0
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Physical properties
Hardness: 6 (Mohs), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal Structure: Aphanitic (fine-grained), 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 during volcanic activity.
Uses & applications
Used primarily in construction (crushed stone, concrete aggregate, road base) and occasionally in art or as industrial flooring.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor, as well as the lunar maria on the Moon.
Field identification & locations
Identify in the field by its dark color, high density, and lack of visible crystals. It is ubiquitous in volcanic regions such as Hawaii, Iceland, and the Pacific Northwest.
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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