igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0. This specimen appears dark, dense, and fine-grained with some crystalline inclusions.

Hardness: 6-7 Mohs
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. It can range in age from modern volcanic flows to billions of years old.

Uses & applications

Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and in the manufacturing 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 extensively on the Moon and Mars.

Field identification & locations

Identify in the field by its heavy weight (density), dark color, and lack of visible quartz. It is commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.

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