igneous

Basalt (Weathered)

Mafic Igneous Rock

Hardness: 5-6 (Mohs), Color: Dark grey to brownish-tan when weathered, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8–3.0

Identified May 24, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs), Color: Dark grey to brownish-tan when weathered, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, 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 specimen appears to be a water-worn or weathered pebble likely from the Cenozoic era.

Uses & applications

Used primarily in construction for road base, concrete aggregate, and railroad ballast. Exceptionally durable for architectural stonework.

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 heavy weight (high density), dark interior color if chipped, and fine-grained texture. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.

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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