igneous

Basalt

Basalt (Aphanitic extrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained, crystals not visible to eye); Cleavage: None (conchoidal or irregular fracture); Specific gravity: 2.8-3.0

Hardness: 6-7 on Mohs scale
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 23, 2026More igneous →

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Physical properties

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 a moon. Most common rock in Earth's crust, found primarily in oceanic crust and huge volcanic plateaus.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and concrete. Also used for high-quality floor tiles, statues, and specialized 'basalt fiber' for industrial applications.

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. On Earth, Olympus Mons on Mars is composed primarily of basaltic lava flows.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and very fine grains. Often shows columnar jointing in large outcrops. Common around volcanic sites, oceanic islands, and rift zones.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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