igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6-7 on Mohs scale; Color: Dark grey to black, weathering to brown or green; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Dark grey to black, weathering to brown or green
Luster: Dull to sub-metallic

Identified April 6, 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 moon. Most basalt on Earth was formed during the Cenozoic era, though it spans all geological ages.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality asphalt. It is also used as a dimension stone for floor tiles and monuments.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also present on the Moon and Mars, where it forms the 'maria' (dark plains).

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows columnar jointing or vesicular (pitted) surfaces in natural outcrops.

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