igneous

Porphyritic Basalt (with Amygdules)

Amygdaloidal Porphyritic Basalt

Hardness (6 on Mohs scale), dark grey/greenish basaltic matrix, white plagioclase or zeolite phenocrysts (amygdules), dull to vitreous luster, fine-grained groundmass with visible crystalline inclusions.

Identified May 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed through rapid cooling of mafic lava on the Earth's surface. The white spots represent gas bubbles (vesicles) that were later filled with secondary minerals like quartz, calcite, or zeolites through hydrothermal activity.

Uses & applications

Crushed stone for road construction, railroad ballast, building stone, and occasionally used as decorative garden stone.

Geological facts

Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. The white spots in this specimen are called 'amygdules' from the Greek word for 'almond'.

Field identification & locations

Identify by its dark, heavy fine-grained background speckled with lighter mineral inclusions. Commonly found in volcanic regions such as the Pacific Northwest, Hawaii, or old rift valleys like the Mid-Atlantic region.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral