Vesicular Basalt with Amygdules

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark grey to black groundmass with pink and white inclusions; Luster: Dull/Earthy matrix with Vitreous inclusions; Structure: Aphanitic with vesicles filled by secondary minerals.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava. The holes (vesicles) were created by gas bubbles, which later filled with secondary minerals like zeolite, calcite, or quartz during hydrothermal activity.

Uses & Applications

Mainly used as decorative stone in landscaping, aquarium decor, or as a geological teaching specimen. Basalt itself is a common aggregate in construction.

Geological Facts

The word 'Amygdule' comes from the Greek word for 'almond', referring to the almond-like shape of the mineral fillings. This rock provides a history of both the volcanic eruption and the later groundwater movement through the area.

Field Identification & Locations

Identify by looking for a dark, heavy fine-grained matrix containing distinct rounded or oval pockets of different colored minerals. Common in volcanic regions such as the Pacific Northwest or Lake Superior region.

Identified on: 4/29/2026

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