igneous

Vesicular Basalt

Basalt (Extrusive Igneous Rock)

Hardness: 5-6 Mohs. Color: Dark grey to black, weathering to brown. Luster: Dull to sub-metallic. Crystal Structure: Fine-grained/aphanitic with vesicular cavities. Specific Gravity: 2.8–3.0.

Hardness: 5-6 Mohs
Color: Dark grey to black, weathering to brown
Luster: Dull to sub-metallic

Identified April 6, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs. Color: Dark grey to black, weathering to brown. Luster: Dull to sub-metallic. Crystal Structure: Fine-grained/aphanitic with vesicular cavities. Specific Gravity: 2.8–3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. The 'vesicles' are holes created by gas bubbles escaping the lava during solidification.

Uses & applications

Used extensively in construction as aggregate for concrete and asphalt, road base, railroad ballast, and sometimes as a decorative landscape stone or 'lava rock' for grills.

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 dark color, heavy weight (density), and the presence of small holes or pits. Commonly found in volcanic regions like the Pacific Northwest, Hawaii, and Iceland.

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