Rock Identifier

igneous

Basalt

Basalt (Aphanitic-to-porphyritic mafic volcanic rock)

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull to sub-metallic (when fresh); Structure: Fine-grained/Aphanitic (crystals not visible to the naked eye); Specific Gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to charcoal black
Luster: Dull to sub-metallic (when fresh)

Identified March 22, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull to sub-metallic (when fresh); Structure: Fine-grained/Aphanitic (crystals not visible to the naked eye); Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic) at or very near the Earth's surface. It is the most common rock in Earth's crust, primarily making up the ocean floors.

Uses & applications

Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality varieties are used for floor tiles, monuments, and stone carvings.

Geological facts

Basalt is not only the most common rock on Earth but also dominates the lunar maria (the dark patches on the moon) and much of the surface of Mars and Venus.

Field identification & locations

Identify by its heavy weight (relative to size), dark color, and fine-grained texture. It often shows 'vesicular' holes (trapped gas bubbles). Common in volcanic regions like the Pacific Northwest, Hawaii, and Iceland.

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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)