igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic), often contains small crystals of olivine or pyroxene; Specific gravity: 2.8–3.0.

Hardness: 6-7 Mohs
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 14, 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. It is the most common volcanic rock on Earth, making up most of the ocean floor.

Uses & applications

Extensively used in construction as aggregate for roads and concrete, as railroad ballast, and occasionally for high-durability floor tiles or monuments.

Geological facts

Basalt is not only the most common rock on Earth's crust, but it is also the primary rock type found on Mars, the Moon, and Venus. Famous basaltic formations include the Giant's Causeway in Northern Ireland.

Field identification & locations

Identification involves looking for a fine-grained, heavy, dark-colored rock that may have small holes (vesicles) or visible green olivine crystals. It is ubiquitous in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

Other igneous specimens

See all

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