igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6.0 (Mohs); Color: Dark gray to black (weathering to tan/brown); Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0

Hardness: 6
Color: Dark gray to black (weathering to tan/brown)
Luster: Dull to sub-metallic

Identified February 8, 2026More igneous →

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Physical properties

Hardness: 6.0 (Mohs); Color: Dark gray to black (weathering to tan/brown); Luster: Dull to sub-metallic; 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 at the surface of a planet. Most common rock in Earth's crust, found in oceanic crust and continental flood basalts.

Uses & applications

Widely used as aggregate in construction, road base, concrete, and railroad ballast. Some varieties are used for stone sculpture and heat-retaining stones in spas.

Geological facts

Basalt is the most common rock type on the Moon's surface and the Martian surface. It often forms striking hexagonal columns during cooling, such as at the Giant's Causeway.

Field identification & locations

Identify by its heavy weight, dark interior, and fine-grained texture that lacks visible crystals. Commonly found in volcanic regions and along oceanic ridges.

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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