igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.

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

Identified April 1, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava. It is the most common rock in Earth's crust, primarily composed of the ocean floors.

Uses & applications

Used extensively in construction as an aggregate for roads, railroad ballast, and concrete; also used as a dimension stone and in high-performance insulation (rock wool).

Geological facts

Basalt covers more than 70% of the Earth's surface. It is also found on the Moon, Mars, and Venus, making up the vast majority of the lunar maria (dark plains).

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible crystals. It typically has a uniform, fine-grained texture and may contain small vesicles (gas bubbles).

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