Igneous

Basalt

Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic when fine-grained, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0.

Identified March 23, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic when fine-grained, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic) at or very near the Earth's surface. Occurs in lava flows across all geological ages on Earth, the Moon, and Mars.

Uses & applications

Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Specifically utilized in industrial 'basalt fiber' and high-end floor tiles.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up the entirety of the ocean floor and found in massive continental flood basalt provinces like the Deccan Traps.

Field identification & locations

Identify by its heavy weight, dark color, and lack of visible crystals (unless porphyritic). Commonly found in volcanic regions. Tip: Look for a fine-grained, 'salt and pepper' or uniform dark appearance that does not scratch easily with steel.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral