igneous

Basalt

Basalt (composition of plagioclase feldspar and pyroxene)

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained/microcrystalline); Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 6
Color: Dark grey to black
Luster: Dull to earthy

Identified May 18, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained/microcrystalline); Cleavage: None; 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 surface. It is the most common volcanic rock on Earth.

Uses & applications

Used primarily in construction for road base, concrete aggregate, railroad ballast, and as a raw material for stone wool insulation.

Geological facts

Basalt makes up most of the Earth's oceanic crust and is also found on the Moon and Mars. It can form unique geometric columns called columnar jointing.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and lack of visible grains. It is commonly found in volcanic regions and ocean floor outcroppings.

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