Rock Identifier

igneous

Basalt

Mafic Volcanic Rock (composed of Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained, crystals not visible to naked eye); Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified March 23, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained, crystals not visible to naked eye); 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. Found on every continent and making up much of the ocean floor; ages range from modern eruptions to billions of years old.

Uses & applications

Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used in high-quality floor tiles and as a raw material for stone wool insulation.

Geological facts

Basalt is the most common rock type in Earth's crust and also covers large portions of the surfaces of the Moon, Mars, and Venus. Famous formations include the Giant's Causeway in Northern Ireland and the Devils Postpile in California.

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible crystals. It typically won't scratch with a steel knife but can be scratched by quartz. Commonly found in volcanic regions or as weathered river stones.

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Blue Apatite (Fluorapatite (Ca5(PO4)3F)) — mineral

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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

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.

Magnetite (Iron(II,III) oxide (Fe3O4)) — mineral

Magnetite

Iron(II,III) oxide (Fe3O4)

Sodalite (Sodalite - Na8(Al6Si6O24)Cl2) — mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

Blue Apatite (Apatite (Group), Ca5(PO4)3(F,Cl,OH)) — mineral

Blue Apatite

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

Magnetite (Magnetite (Fe3O4)) — mineral

Magnetite

Magnetite (Fe3O4)