Rock Identifier

igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained crystals generally not visible to the naked eye); Specific gravity: 2.8-3.0.

Hardness: 6 (Mohs scale)
Color: Dark grey to black, weathering to brown
Luster: Dull to sub-metallic

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained crystals generally not visible to the naked eye); Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Basalts occur in all geological ages from the Archean to the Holocene.

Uses & applications

Used extensively in construction as road aggregate, railroad ballast, and in concrete. It is also used as dimension stone for tiles and facades, and occasionally in jewelry as ornmental stone.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale areas of basalt are known as flood basalts, such as the Deccan Traps or Columbia River Basalt Group.

Field identification & locations

Identify by its heavy weight (density), dark color, and fine-grained texture. Found globally in volcanic regions. Look for small holes called vesicles which may contain secondary minerals.

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Dark Igneous Rock (Likely Basalt or Diabase)

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Magnetite (Iron(II,III) oxide (Fe3O4)) — mineral

Magnetite

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Blue Apatite (Apatite (Group), Ca5(PO4)3(F,Cl,OH)) — mineral

Blue Apatite

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Sodalite (Sodalite - Na8(Al6Si6O24)Cl2) — mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

Magnetite (Magnetite (Fe3O4)) — mineral

Magnetite

Magnetite (Fe3O4)