igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black, greenish-black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.

Hardness: 6 on Mohs scale
Color: Dark grey to black, greenish-black
Luster: Dull to sub-metallic

Identified April 11, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to black, greenish-black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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. This specific specimen appears to be a river-worn cobble, rounded by water erosion.

Uses & applications

Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-density basalt is used for coastal protection.

Geological facts

Basalt is the most common rock type on 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 by its dark color, heavy weight (high density), and fine-grained texture. To confirm, look for the absence of visible quartz crystals and a rounded, water-worn exterior if found near rivers.

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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