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

Identified March 22, 2026More igneous →

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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.

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mineral

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