igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6.0; Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic) microcrystalline; Cleavage: None; Specific Gravity: 2.8 - 3.0

Hardness: 6
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified May 9, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic) microcrystalline; Cleavage: None; Specific Gravity: 2.8 - 3.0

Formation & geological history

Formed through the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the Earth's surface. Common in oceanic crust and volcanic islands.

Uses & applications

Used primarily in construction for road base, concrete aggregate, railroad ballast, and occasionally as structural stone or in the manufacture of stone wool insulation.

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 and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in regions with volcanic history or near coastal basalt columns.

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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