igneous

Basalt (Weathered Pebble)

Extrusive mafic rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 5-6 (Mohs scale); Color: Dark grey to charcoal with micro-crystalline texture; Luster: Dull/Earthy (weathered); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.

Hardness: 5-6 (Mohs scale)
Color: Dark grey to charcoal with micro-crystalline texture
Luster: Dull/Earthy (weathered)

Identified March 7, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs scale); Color: Dark grey to charcoal with micro-crystalline texture; Luster: Dull/Earthy (weathered); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the Earth's surface. These specific specimens are water-worn 'river rocks' or beach pebbles, likely from the Cenozoic era or older volcanic flows.

Uses & applications

Used extensively in construction as road base, aggregate in concrete, and railroad ballast. Exceptionally durable for landscaping and stone carvings.

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 a major component of the lunar maria on the Moon and the surface of Mars.

Field identification & locations

Identify in the field by its dark color, heavy weight for its size, and the absence of visible large crystals. Commonly found in volcanic regions, coastal areas, and ancient lava beds. Collectors look for 'vesicular' basalt which contains gas bubbles.

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

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