igneous

Basalt

Basalt (containing Pyroxene, Plagioclase feldspar, and Olivine)

Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull/submetallic; Crystal Structure: aphanitic (fine-grained); Cleavage: none; Specific Gravity: 2.8 - 3.0

Hardness: 6-7 Mohs
Color: dark grey to black
Luster: dull/submetallic

Identified May 3, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull/submetallic; Crystal Structure: aphanitic (fine-grained); 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's surface. Common in oceanic crust and volcanic islands.

Uses & applications

Used primarily in construction for road base, concrete aggregate, and railroad ballast. Also used as dimension stone and in high-tensile industrial fibers.

Geological facts

Basalt is the most common rock type in the Earth's crust and also covers large areas of Mars and the Moon (lunar maria).

Field identification & locations

Identify in the field by its dark color, high density, and fine-grained texture with occasional small green olivine crystals. Found globally in volcanic regions.

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