igneous
Basalt
Basalt (composition primarily Plagioclase Feldspar and Pyroxene)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; 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. Most specimens are from the Cenozoic era, though it has formed throughout Earth's history.
Uses & applications
Extensively used in construction as aggregate for concrete and asphalt, road base, railroad ballast, and occasionally as decorative landscaping stone or architectural stone.
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.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. It often appears as rounded river cobbles or geometric columns in the field. Found globally in volcanic regions.
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Blue Apatite
Fluorapatite (Ca5(PO4)3F)
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Dalmatian Jasper
Aplite with Arfvedsonite inclusions
igneous
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
Magnetite
Iron(II,III) oxide (Fe3O4)
mineral