igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6 on Mohs scale; Color: Dark grey to greenish-black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained), often containing micro-crystals of plagioclase feldspar and pyroxene; Cleavage: None (conchoidal fracture); Specific gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: Dark grey to greenish-black
Luster: Dull to earthy

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. This specific specimen shows signs of weathering and redondeon, likely from fluvial (river) transport.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Characterized by high compressive strength and durability. Some fine-grained varieties are used for stone tools or decorative garden stones.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also found on the Moon and Mars—the dark plains of the Moon (the Maria) are composed of basaltic lava flows.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and fine-grained texture that lacks visible large crystals to the naked eye. Commonly found in volcanic regions, oceanic islands (like Hawaii), and riverbeds near volcanic mountain ranges.

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