igneous

Amygdaloidal Basalt

Hardness (typical): 6 on Mohs scale; Color: dark grey to brownish-purple groundmass with white/light-colored spots; Luster: dull to earthy matrix with vitreous inclusions; Crystal structure: aphanitic; Cleavage: none.

Luster: dull to earthy matrix with vitreous inclusions

Identified June 3, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the cooling of gas-rich lava flows. Voids created by gas bubbles (vesicles) are later filled with secondary minerals like calcite, quartz, or zeolites through groundwater precipitation. Often found in Proterozoic volcanic sequences.

Uses & applications

Used primarily as decorative landscaping stones, aquarium decor, and as a geological study aid. Occasional specimens with semi-precious fillings can be used for cabochons.

Geological facts

The word 'Amygdule' comes from the Greek word for 'almond,' referring to the shape of the mineral-filled cavities. It is very common in the Lake Superior region of North America.

Field identification & locations

Identify in the field by looking for a dark, dense volcanic rock containing distinct almond-shaped spots or 'pores' filled with light minerals. Found in areas of past volcanic activity.

Other igneous specimens

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Granite

Igneous

Granite

Igneous

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

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