igneous

Basalt River Pebble

Mafic Igneous Rock (Fine-grained Basalt)

Hardness: 6-7 on Mohs scale. Color: Dark gray to greenish-gray. Luster: Dull or earthy. Structure: Fine-grained (aphanitic), non-crystalline visible to the naked eye. Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Dark gray to greenish-gray
Luster: Dull or earthy

Identified March 9, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Dark gray to greenish-gray. Luster: Dull or earthy. Structure: Fine-grained (aphanitic), non-crystalline visible to the naked eye. 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 has been water-worn and weathered in a fluvial (river) or coastal environment, giving it its smooth, rounded shape.

Uses & applications

Primarily used in construction as aggregate, road base, and concrete. In smaller forms like this, it is used for decorative landscaping, 'worry stones', or 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 on the Moon and Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight relative to size (high density), and lack of visible crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic sources. Collectors value specimens with unique weathering patterns.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral