Igneous

Vesicular Basalt

Amygdaloidal Basalt (Mafic extrusive volcanic rock)

Hardness: 5-6 (Mohs); Color: Dark grey to reddish-brown (weathered) with light-colored mineral infills; Luster: Dull (extrusive) to vitreous (minerals); Structure: Vesicular/Aphanitic; Cleavage: None/Irregular

Hardness: 5-6 (Mohs)
Luster: Dull (extrusive) to vitreous (minerals)

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. The holes (vesicles) were formed by gas bubbles trapped in the lava during eruption. Amygdules form when secondary minerals like zeolites or calcite precipitate in these voids over millions of years.

Uses & applications

Used primarily in construction as crushed stone, road base, or concrete aggregate. Vesicular varieties are often used in landscaping (lava rock) and occasionally for geological education/collection.

Geological facts

Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found on the Moon and Mars, forming the dark plains known as 'maria'.

Field identification & locations

Identify by its dark color, heavy weight, and distinct 'sponge-like' holes. Found in volcanic regions like the Pacific Northwest (USA), Iceland, and Hawaii. In the field, look for 'frothy' textures near volcanic vents.

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