igneous

Basalt

Basalt (Mafic igneous rock)

Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.

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

Identified May 3, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); 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 aggregate for roads and concrete, in railroad ballast, and sometimes carved for decorative sculptures or tiles.

Geological facts

Basalt is the most common rock on Earth's surface, making up most of the ocean floor and major volcanic islands like Hawaii and Iceland.

Field identification & locations

Identified in the field by its dark color, high density, and fine-grained texture. It often shows vesiculation (small holes) or columnar jointing in large outcrops.

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