Rock Identifier

igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline/Aphanitic (crystals too small to see with the naked eye); Specific Gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Black to dark gray
Luster: Dull to sub-metallic

Identified April 10, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline/Aphanitic (crystals too small to see with the naked eye); Specific Gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the surface. It is the most common volcanic rock on Earth and major planetary bodies like the Moon and Mars.

Uses & applications

Extensively used in construction as an aggregate (crushed stone) for road bases, concrete, and railroad ballast. It is also used as dimension stone for tiles and in the production of stone wool insulation.

Geological facts

Basalt covers approximately 70% of Earth's surface in the form of oceanic crust. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt jointing caused by the cooling and contraction of thick lava flows.

Field identification & locations

Identify by its heavy weight (density), dark color, and fine-grained texture. It often shows 'vesicles' (gas bubbles) or may be solid. Found in volcanic regions and ocean basins worldwide.

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Dark Igneous Rock (Likely Basalt or Diabase)

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Magnetite (Magnetite (Fe3O4)) — mineral

Magnetite

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