igneous

Basalt

Mafic volcanic rock (consisting mostly of plagioclase, pyroxene, and olivine)

Hardness: 6 on Mohs scale; Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: Dark grey to black, often weathering to brown
Luster: Dull to sub-metallic

Identified March 28, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to black, often weathering to 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 exposed at or very near the surface of a terrestrial planet or a moon. It covers about 70% of Earth's surface through oceanic crust.

Uses & applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. High-quality specimens are used in stone carving and as semi-precious 'lava stones' in jewelry.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up the giant lunar maria on the Moon. It can form unique hexagonal columns when cooling slowly, such as the Giant's Causeway.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture with no visible large crystals. Commonly found in volcanic regions, oceanic islands (Hawaii, Iceland), and tectonic rift zones.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral