igneous

River Rock (Basalt)

Aphanitic Basaltic Rock

Hardness: 6.0-7.0 (Mohs scale). Color: Medium to dark grey. Luster: Dull/earthy (weathered surface). Structure: Microcrystalline to aphanitic (fine-grained). Cleavage: None. Specific Gravity: 2.8-3.0.

Hardness: 6
Color: Medium to dark grey
Luster: Dull/earthy (weathered surface)

Identified March 22, 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 very near the Earth's surface. This specific specimen has been transport-weathered and rounded through fluvial (river) or glacial action, likely over thousands of years.

Uses & applications

Commonly used in landscaping (mulch replacement), drainage systems, construction aggregate, and occasionally for rock painting or spa 'hot stones'.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basaltic lava flows can form unique hexagonal columns, such as those at the Giant's Causeway.

Field identification & locations

Identify in the field by its heavy weight (high density), dark interior color, and smooth, water-worn texture. It is a 'clastic' river stone found in stream beds, beaches, and landscaping supply yards globally.

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