igneous

Basalt (River Pebble)

Basalt (dominated by Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0. This specimen is rounded due to fluvial erosion.

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull/Matte

Identified February 19, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0. This specimen is rounded due to fluvial erosion.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. As an extrusive igneous rock, it is often associated with volcanic activity and oceanic crust formation.

Uses & applications

Commonly used in construction as aggregate for concrete and asphalt, railroad ballast, and ground cover in landscaping. Dense specimens are also used for hot stone massage therapy.

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, where it forms the dark 'maria' (seas) visible from Earth.

Field identification & locations

Identify in the field by its dark color, heavy weight for its size, and lack of visible crystals to the naked eye. In riverbeds, look for smooth, dark, rounded stones that do not scratch easily with steel.

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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