igneous

Basalt

Basalt (Aphanitic Mafic Volcanic Rock)

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull (earthy) to sub-metallic; Structure: Fine-grained (aphanitic) or porphyritic; Cleavage: None; Specific Gravity: 2.8 - 3.0

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

Identified March 18, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull (earthy) to sub-metallic; Structure: Fine-grained (aphanitic) or porphyritic; 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 a moon. It can be found in various geological ages, from recent volcanic flows to billions of years old.

Uses & applications

Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used in high-quality floor tiles, 'stone wool' insulation, and occasionally for carved monuments or sculptures.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also common on the Moon (forming the 'maria' or dark plains) and Mars. Some basalt cools into striking hexagonal columns, like at the Giant's Causeway in Ireland.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture where individual crystals are too small to see with the naked eye. Often found near volcanic hotspots, mid-ocean ridges, and continental rift zones.

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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