igneous

Basalt

Basalt (primarily composed of Plagioclase Feldspar and Pyroxene)

Hardness: 6-7 (Mohs); Color: Dark grey to black, weathering to brown; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Hardness: 6-7 (Mohs)
Color: Dark grey to black, weathering to brown
Luster: Dull or earthy

Identified March 26, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs); Color: Dark grey to black, weathering to brown; Luster: Dull or earthy; 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 or very near the Earth's surface. Common in oceanic crust and volcanic regions; ages range from modern to billions of years old.

Uses & applications

Extensively used in construction as an aggregate (crushed stone) for roads, railroad ballast, and concrete. Also used in high-quality floor tiles and monuments.

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 dark color, heavy weight (density), and fine-grained texture with no visible crystals to the naked eye. Commonly found in coastal areas or old volcanic plateaus. Collectors look for vesicles (holes) which may contain secondary minerals like zeolites or semi-precious gems.

Other igneous specimens

See all

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