igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black, sometimes greenish due to olivine; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black, sometimes greenish due to olivine
Luster: Dull to sub-metallic

Identified March 1, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, sometimes greenish due to olivine; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; 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 a moon. Most common in oceanic crust and mid-ocean ridges.

Uses & applications

Used primarily in construction for aggregate, road base, concrete, and railroad ballast. Also used as stone for countertops, floor tiles, and garden statuary.

Geological facts

Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars (Lunar Maria are composed of basaltic lava flows).

Field identification & locations

Identify by its dark color, heavy weight (high density), and lack of visible crystals. Commonly found in volcanic regions, near oceanic ridges, and in large flood basalt provinces. Use a magnet to check for magnetite content.

Other igneous specimens

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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