igneous

Basalt

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained), often containing microcrystals of plagioclase feldspar and pyroxene; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8-3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 19, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic lava) exposed at or very near the surface of a terrestrial planet or a moon. Most common rock type in the Earth's crust, primarily forming the ocean floor.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and concrete. It is also used as dimension stone for pavers and monuments, and finely ground as a soil amendment or in the production of stone wool insulation.

Geological facts

Basalt is the most common volcanic rock on Earth and also makes up large portions of the surfaces of the Moon, Mars, and Venus. The famous Giant's Causeway in Ireland is composed of columnar basalt pillars.

Field identification & locations

Identify in the field by its heavy weight (density), dark color, and fine-grained texture. It often shows a 'frosted' or dull weathered surface. It is commonly found in volcanic regions, oceanic islands (like Hawaii), 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