igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6-7 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Hardness: 6-7 (Mohs)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified April 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and continental flood basalt provinces.

Uses & applications

Extensively used in construction as aggregate (crushed stone), road base, railroad ballast, and sometimes in high-quality floor tiles or as 'hot stones' for massage therapy.

Geological facts

Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon and Mars, forming the large dark plains known as 'maria'.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and fine-grained texture that lacks visible crystals to the naked eye. Often found in volcanic regions or as rounded river/beach pebbles.

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