igneous

Basalt

Basalt (Mafic igneous rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0; Cleavage: None, often demonstrates concoidal fracture.

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

Identified June 1, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface. It is the most common rock in Earth's crust, primarily forming oceanic plates and large volcanic flows.

Uses & applications

Extensively used in construction as aggregate for roads and concrete, railroad ballast, and sometimes as a dimension stone for floor tiles or monument bases.

Geological facts

Basalt is the primary rock type on the Moon's lunar maria and also composes the majority of the Martian surface. It can form unique towering hexagonal structures known as columnar jointing.

Field identification & locations

Identify in the field by its high density, dark color, and very fine-grained texture which makes individual crystals difficult to see without a lens. Often found in volcanic regions or coastal cliffs.

Other igneous specimens

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Granite

Igneous

Granite

Igneous

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral