igneous

Basalt Pebble

Basalt (Mafic Volcanic Rock)

Hardness: 6 (Mohs); Color: Dark gray to black, often weathering to brown; Luster: Dull or earthy when weathered; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0

Hardness: 6 (Mohs)
Color: Dark gray to black, often weathering to brown
Luster: Dull or earthy when weathered

Identified May 24, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark gray to black, often weathering to brown; Luster: Dull or earthy when weathered; 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 near the Earth's surface. This specimen appears water-worn from fluvial or coastal transport.

Uses & applications

Crushed basalt is used in construction (base for roads/railroads) and as an aggregate in concrete; polished pebbles are used in landscaping and aquariums.

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 by its dark color, heavy weight (density), and lack of visible large crystals. In the field, basalt is common in volcanic regions and riverbeds.

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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