igneous

Basalt

Basalt (Igneous Volcanic Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: Non-existent; Specific Gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull/Matte

Identified April 3, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: Non-existent; 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 Earth's surface. Common in oceanic crust and huge volcanic plateaus.

Uses & applications

Extensively used in construction as aggregate for concrete and asphalt, road base, railroad ballast, and sometimes as dimension stone or floor tiles.

Geological facts

Basalt is the most common rock type in Earth's crust and also identifies the composition of the lunar maria on the Moon and much of the surface of Mars.

Field identification & locations

Identify by its dark color, heavy weight (high density), and very fine-grained texture that lacks visible crystals. Often shows 'vesicles' (gas bubbles) or columnar jointing in the field. Found globally in volcanic regions.

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