igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular; Specific gravity: 2.8–3.0.

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

Identified April 11, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular; Specific gravity: 2.8–3.0.

Formation & geological history

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

Uses & applications

Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as dimension stone for tiles and landscape features.

Geological facts

Basalt is the most common rock on Earth's surface and also covers large areas of the Moon (the lunar maria) and Mars.

Field identification & locations

Field ID: Look for dark color, heavy weight (dense), and fine-grained texture. It may contain small holes called vesicles or form hexagonal columns. Common in oceanic islands like Hawaii or Iceland.

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