igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic) or porphyritic; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0.

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

Identified March 30, 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 of a terrestrial planet or a moon. Most common rock on Earth's crust, primarily forming at mid-ocean ridges.

Uses & applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. High-quality basalt (scoria) is used in landscaping. Some varieties are used for stone tools or thermal insulation (stone wool).

Geological facts

Basalt is the most common rock type in the Earth's crust (the ocean floor is almost entirely basalt). It is also found on the Moon and Mars, where it forms the lunar maria (the dark plains visible from Earth).

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture where individual crystals are not visible to the naked eye. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

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