Igneous

Basalt River Pebble

Extrusive mafic igneous rock; primarily composed of Plagioclase Feldspar and Pyroxene

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to waxy when polished; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; No visible cleavage in hand specimen.

Hardness: 6-7 on Mohs scale
Color: Dark grey to black
Luster: Dull to waxy when polished

Identified March 25, 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 specific specimen has been rounded and smoothed by fluvial (river) or marine erosion over hundreds to thousands of years.

Uses & applications

Commonly used in landscaping, as decorative 'river stones,' in construction aggregate, and frequently in hot stone massage due to its high heat retention properties.

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, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight for its size, and the lack of visible crystals. Commonly found in riverbeds, beaches, and volcanic fields worldwide. Collectors should look for unique shapes or vesicles (gas bubbles).

Other igneous specimens

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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

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral