Igneous

Basalt (with possible weathering or secondary mineral crust)

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black, with tan/brown weathered crust; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Specific gravity: 2.8-3.0.

Hardness: 6 (Mohs scale)
Color: Dark grey to black, with tan/brown weathered crust
Luster: Dull to sub-metallic

Identified March 22, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, with tan/brown weathered crust; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Specific gravity: 2.8-3.0.

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 to have an oxidized exterior or 'desert varnish' common in volcanic fields.

Uses & applications

Commonly used as aggregate in construction (roads and concrete), as paving stones, and sometimes for high-end landscaping or 'lava stones' in grilling.

Geological facts

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

Field identification & locations

Identify by its heavy weight (density), dark interior, and fine-grained texture where individual crystals are too small to see with the naked eye. Found globally in volcanic regions like Hawaii, the Pacific Northwest, or Iceland.

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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