igneous

Basalt with Vesicular Texture (Beach Cobble)

Vesicular Basalt (Aphanitic Igneous Rock)

Hardness: 5-6 (Mohs); Color: Reddish-brown (oxidized) to dark grey; Luster: Dull/Earthy; Crystal structure: Microcrystalline (aphanitic); Cleavage: None/Irregular; Specific Gravity: 2.8–3.0.

Hardness: 5-6 (Mohs)
Color: Reddish-brown (oxidized) to dark grey
Luster: Dull/Earthy

Identified March 21, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Reddish-brown (oxidized) to dark grey; Luster: Dull/Earthy; Crystal structure: Microcrystalline (aphanitic); Cleavage: None/Irregular; 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. The 'pits' are vesicles caused by gas bubbles trapped as the lava solidified. The reddish hue indicates oxidation of iron minerals (hematite/magnetite) over geological time.

Uses & applications

Commonly used as construction aggregate, road base, and for landscaping stone. High-quality scoria or basalt is sometimes used in 'lava rock' grilling or as filter media.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The rounded shape of this specimen indicates it has been tumbled by water in a river or beach environment.

Field identification & locations

Identify in the field by its heavy weight (high density), dark matrix, and small holes (vesicles). It is frequently found on volcanic islands and coastal areas near tectonic plate boundaries.

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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.

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Iron(II,III) oxide (Fe3O4)

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Magnetite

Magnetite (Fe3O4)

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