igneous

Basalt with Vesicular Surface

Basalt (Mafic Extrusive)

Hardness: 6.0; Color: Dark gray to black, often weathering to tan/brown; Luster: Dull/earthy to sub-metallic; Structure: Fine-grained (aphanitic) with small pits or vesicles; Specific Gravity: 2.8–3.0.

Hardness: 6
Color: Dark gray to black, often weathering to tan/brown
Luster: Dull/earthy to sub-metallic

Identified April 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen appears weathered and may contain secondary mineral infilling in its pores.

Uses & applications

Commonly used as aggregate in construction, road base, concrete, and railroad ballast. Highly weathered or high-quality specimens are occasionally used in landscape design.

Geological facts

Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows 'vesicles' (gas bubble holes) or a rusty exterior from iron oxidation. Found worldwide in volcanic regions.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Magnetite

Magnetite (Fe3O4)

mineral