igneous

Basalt with Secondary Mineral Inclusions

Amygdaloidal Basalt (Mafic volcanic rock, primarily Augite and Plagioclase)

Hardness: 6.0-7.0 (Mohs); Color: Dark grey to charcoal with reddish oxide staining; Luster: Dull, earthy matrix with vitreous inclusions; Structure: Fine-grained aphanitic matrix; Specific Gravity: 2.8-3.0.

Hardness: 6
Color: Dark grey to charcoal with reddish oxide staining
Luster: Dull, earthy matrix with vitreous inclusions

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The vesicular or 'pitted' texture suggests gas bubbles were trapped during cooling, later potentially filled by secondary minerals (amygdules) like quartz or calcite.

Uses & applications

Common basalt is used extensively in construction as aggregate for roads and railways, and in high-strength concrete. Rare or mineral-rich specimens are kept for geological study and private collections.

Geological facts

Basalt is the most common rock type on the Earth's surface and makes up most of the ocean floor. It is also prevalent on Mars and the Moon.

Field identification & locations

Identify by its heavy weight (high density), dark color, and fine crystalline grain. Commonly found in volcanic regions such as the Pacific Northwest, Iceland, and Hawaii. Look for 'vuggy' or holey textures that indicate volcanic gas escape.

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