igneous

Basalt with Vesicular Texture

Extrusive Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 6 on Mohs scale; Color: Dark grey to bluish-grey; Luster: Dull (earthy); Crystal structure: Aphanitic (fine-grained) with visible vesicles (pitted surface); Specific gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: Dark grey to bluish-grey
Luster: Dull (earthy)

Identified March 8, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to bluish-grey; Luster: Dull (earthy); Crystal structure: Aphanitic (fine-grained) with visible vesicles (pitted surface); 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. It is the most common rock in Earth's crust, making up most of the ocean floor. Common in volcanic regions.

Uses & applications

Used extensively in construction as road base, railroad ballast, and aggregate in concrete. It is also used for cobblestones and sometimes as a thermal insulator in its mineral wool form.

Geological facts

Basalt is also found on other planetary bodies, including the Moon, Mars, and Venus. On the Moon, the dark plains known as 'Maria' are composed of massive basaltic lava flows.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often breaks into sharp edges. It is extremely common in the Pacific Northwest of the US, Iceland, and Hawaii.

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