igneous

Basalt

Basalt (Mafic Volcanic Rock)

Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull or earthy; Crystal Structure: Aphanitic (fine-grained); Cleavage: Non-existent; Specific Gravity: 2.8–3.0

Hardness: 5-6 (Mohs)
Color: Dark gray to black
Luster: Dull or earthy

Identified March 31, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull or earthy; Crystal Structure: Aphanitic (fine-grained); Cleavage: Non-existent; Specific Gravity: 2.8–3.0

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 commonly found at mid-ocean ridges or volcanic hotspots.

Uses & applications

Extensively used in construction as aggregate (crushed stone), for concrete and asphalt, and occasionally for high-durability floor tiles or dimension stone.

Geological facts

Basalt is the most common rock type in the Earth's crust, covering most of the ocean floor. It is also found on the Moon and Mars.

Field identification & locations

Identify by its dark color, fine-grained texture, and high density. Commonly found in volcanic regions like Hawaii, Iceland, or the Columbia River Plateau. Use a magnet to check for titanomagnetite grains.

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