Igneous

Basalt (Vesicular/Scoriaceous)

Extrusive Mafic Volcanic Rock (Primarily Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale), Color: Dark grey to black or brownish-black, Luster: Dull/Sub-metallic, Structure: Fine-grained (aphanitic), Specific Gravity: 2.8 - 3.0

Identified March 14, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black or brownish-black, Luster: Dull/Sub-metallic, Structure: Fine-grained (aphanitic), Specific Gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen appears water-worn or weathered, indicating transportation in a river or coastal environment from its volcanic source.

Uses & applications

Used extensively in construction as road base, aggregate for concrete, and railroad ballast. In finer specimens, used for decorative landscaping and stone massage therapy.

Geological facts

Basalt is the most common rock on Earth's surface, making up most of the ocean floor and the lunar maria on the Moon. It contains magnetite, which can make some specimens slightly magnetic.

Field identification & locations

Identify by its heavy weight (density), dark color, and fine-grained texture. It often shows 'vesicles' (small holes from trapped gas bubbles). Commonly found in volcanic regions, oceanic islands, and as river cobbles in drainage basins.

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