igneous

Basalt

Basalt (Mafic Extrusive)

Hardness (Mohs): 6.0; Color: Dark grey to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Color: Dark grey to black
Luster: Dull to submetallic

Identified May 16, 2026More igneous →

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Physical properties

Hardness (Mohs): 6.0; Color: Dark grey to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained); 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. Often found in oceanic crust and continental flood basalt provinces.

Uses & applications

Used primarily as aggregate in construction projects, road base, concrete, and railroad ballast. Finer varieties are used for stone monuments or statues.

Geological facts

Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon and Mars. Its dark color comes from its high concentration of pyroxene and olivine minerals.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture that lacks visible crystals. Commonly found in volcanic regions, near ocean ridges, or as glacial erratics.

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