igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal Structure: Fine-grained/Aphanitic, Cleavage: None, Specific Gravity: 2.8-3.0.

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal Structure: Fine-grained/Aphanitic, Cleavage: None, 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. Most basalt is Cenozoic in age but can range back to the Archean.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and as a decorative stone or architectural material.

Geological facts

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

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.

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