igneous

Basalt

Extrusive Mafic Igneous Rock

Hardness: 6 (Mohs scale); Color: Dark gray to black (weathering to brown/green); Luster: Dull/Submetallic; Texture: Fine-grained/Aphanitic; Crystal Structure: Microcrystalline with occasional phenocrysts; Specific Gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black (weathering to brown/green)
Luster: Dull/Submetallic

Identified March 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava at or very near the Earth's surface. It can be found in oceanic crust, mid-ocean ridges, and continental flood basalt provinces varying from Archean to Recent geological ages.

Uses & applications

Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Used in industry for creating basalt fiber and stone wool insulation. Occasionally used in landscaping and architecture.

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 extremely common on other planetary bodies, including the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture that lacks visible crystals. It often breaks with a conchoidal fracture and may show columnar jointing in large outcrops. Common in volcanic regions like Iceland, Hawaii, 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