igneous

Basalt

Basalt (principally Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to earthy; Structure: Aphanitic (fine-grained), often vesicular or massive; Specific Gravity: 2.8–3.0.

Hardness: 6 (Mohs scale)
Color: Dark gray to black
Luster: Dull to earthy

Identified March 18, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to earthy; Structure: Aphanitic (fine-grained), often vesicular or massive; Specific Gravity: 2.8–3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Most specimens are from the Cenozoic era, though occurrences date back billions of years.

Uses & applications

Extensively used in construction as aggregate (crushed stone), for paving roads, railroad ballast, and in the production of stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. It is found globally in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

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