igneous

Basalt

Basalt (containing Pyroxene, Plagioclase Feldspar, and Olivine)

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8 - 3.0.

Hardness: 6
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified February 26, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; 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 can range in age from modern eruptions to billions of years old.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for acid-resistant equipment in chemical industries and occasionally as a decorative stone.

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 (the dark 'Maria' plains) and Mars.

Field identification & locations

Identify by its heavy weight (density), dark color, and very fine-grained texture with no visible quartz. Found in volcanic regions like Iceland, Hawaii, and the Pacific Northwest. Collectors look for vesicular basalt (with holes) or basalt with green olivine inclusions.

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