igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to tan/brown; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), often vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black, weathering to tan/brown
Luster: Dull to sub-metallic

Identified March 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found in tectonic plates, hotspots (like Hawaii), and mid-ocean ridges. Formed throughout Earth's history.

Uses & applications

Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality varieties are used for floor tiles, monuments, and stone carvings.

Geological facts

Basalt is the most common rock type in Earth's crust, covering most of the ocean floor. It is also found on the Moon, Mars, and Venus, making it a primary component of terrestrial planetary surfaces.

Field identification & locations

Identify by its heavy weight (high density), dark color, and lack of visible crystals to the naked eye. Look for tiny holes (vesicles) or a 'salt and pepper' appearance under a hand lens. Commonly found in volcanic fields.

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