igneous

Basalt River Pebble

Basalt

Hardness: 6 on Mohs scale; Color: dark brown to black (weathered); Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8–3.0. Surfaces are smooth and rounded due to water erosion.

Hardness: 6 on Mohs scale
Color: dark brown to black (weathered)
Luster: dull to earthy

Identified June 4, 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 near the Earth's surface. This pebble has been subsequently shaped and smoothed by transport in a high-energy water environment, such as a river or coastal area.

Uses & applications

Commonly used in construction as aggregate, for road base, in landscaping, and occasionally as 'hot stones' for massage therapy due to high heat retention.

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

Identified in the field by its dark color, heavy weight (density), and fine-grained texture. It often lacks visible crystals to the naked eye. This specimen shows classic abiotic rounding from fluvial processing.

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Magnetite

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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