igneous

Basalt

Hardness: 6 on Mohs scale. Color: Dark gray to black. Luster: Dull or matte. Crystal structure: Aphanitic (fine-grained), often with microscopic crystals. Specific gravity: 2.8 - 3.0.

Hardness: 6 on Mohs scale
Color: Dark gray to black
Luster: Dull or matte

Identified April 8, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale. Color: Dark gray to black. Luster: Dull or matte. Crystal structure: Aphanitic (fine-grained), often with microscopic crystals. 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. It is the most common volcanic rock on Earth.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. It is also used as dimension stone for building and in the manufacturing of stone wool insulation.

Geological facts

Basalt is the primary component of the oceanic crust. It also makes up most of the surface of the Moon and Mars. Famous basalt formations include the Giant's Causeway in Northern Ireland and the Devils Postpile in California.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and very fine crystalline texture. It is ubiquitous in volcanic regions and along oceanic islands like Hawaii.

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