igneous

Amygdaloidal Basalt with Secondary Minerals

Basalt containing secondary mineralization (likely Chlorite, Celadonite, or Zeolites)

The matrix is dark gray to reddish-brown (reddening suggests oxidation) with a fine-grained, aphanitic texture. The small round or oval cavities are amygdules filled with green and white minerals. Hardness of the basalt is 5-6 on the Mohs scale. The green minerals typically have an earthy to vitreous luster.

Identified February 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the rapid cooling of lava flows. The gas bubbles (vesicles) trapped in the cooling lava were later filled with secondary minerals such as chlorite, epidote, or celadonite deposited by hydrothermal fluids or groundwater over thousands to millions of years. This specimen appears to be from ancient volcanic activity, possibly dating from the Cenozoic or older platforms.

Uses & applications

Basalt itself is widely used in road construction, as asphalt aggregate, and in railroad ballast. While this specific specimen is more of a geological curiosity for collectors, amygdaloidal basalt is occasionally used as a decorative stone in landscaping. High-quality celadonite or zeolite pockets can be of interest to mineral collectors.

Geological facts

The term 'amygdule' comes from the Latin 'amygdala', meaning almond, because the mineral-filled cavities are often almond-shaped. Large deposits of this rock type in the Lake Superior region of the USA are famous for containing native copper within the amygdules instead of minerals like the ones shown here.

Field identification & locations

In the field, look for a heavy, dark, fine-grained rock containing small rounded 'spots' of differing colors (green, white, or pink). It is common in regions with ancient volcanic activity like the Pacific Northwest, the British Isles, or the Deccan Traps. Collectors can easily spot the contrasting green minerals against the dark basaltic base.

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