igneous
Basalt
Basalt (Mafic Extrusive)
Hardness: 6-7 Mohs; Color: dark gray to black, often weathering to brownish or greenish; Luster: dull to earthy; Crystal Structure: Aphanitic (fine-grained), sometimes porphyritic or vesicular; Specific gravity: 2.8–3.0.
- Hardness
- 6-7 Mohs
- Color
- dark gray to black, often weathering to brownish or greenish
- Luster
- dull to earthy
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Physical properties
Hardness: 6-7 Mohs; Color: dark gray to black, often weathering to brownish or greenish; Luster: dull to earthy; Crystal Structure: Aphanitic (fine-grained), sometimes porphyritic or vesicular; 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. It comprises over 90% of all volcanic rock on Earth and forms the bulk of the ocean floor.
Uses & applications
Extensively used in construction as aggregate for roads and concrete, railroad ballast, and high-quality stone for floor tiles and monuments. Some varieties are used in 'stone washing' textiles or as industrial insulation (basalt fiber).
Geological facts
Basalt is the most common rock in the solar system, covering vast areas of the Moon, Mars, and Venus. On Earth, it often forms striking columnar jointing patterns, like the Giant's Causeway.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture where individual crystals are not visible to the naked eye. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
