Igneous
Basalt
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal structure: Aphanitic (fine-grained, invisible to naked eye); Cleavage: None; Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull or sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal structure: Aphanitic (fine-grained, invisible to naked eye); Cleavage: None; Specific Gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. It is the most common rock in the Earth's crust, forming the bulk of the ocean floor and large continental provinces.
Uses & applications
Extensively used in construction for aggregate in road bases, concrete, and asphalt; also used for railroad ballast and dimension stone for paving blocks or tiles.
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up a significant portion of the surfaces of the Moon, Mars, and Venus. On the Moon, the dark plains known as 'Maria' are composed of ancient basaltic lava flows.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows small holes called vesicles trapped by gas bubbles. It is found globally along mid-ocean ridges, volcanic islands, and continental volcanic fields.
