igneous
Vesicular Basalt (Amygdaloidal)
Amygdaloidal Basalt
Hardness: 6-7. Color: Purplish-red Matrix with white mineral inclusions. Luster: Dull to sub-vitreous. Structure: Vesicular/Aphanitic with amygdules. Specific Gravity: 2.8-3.0.
- Hardness
- 6-7
- Color
- Purplish-red Matrix with white mineral inclusions
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7. Color: Purplish-red Matrix with white mineral inclusions. Luster: Dull to sub-vitreous. Structure: Vesicular/Aphanitic with amygdules. Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of basaltic lava. The holes (vesicles) were created by gas bubbles, which later became filled with secondary minerals like quartz, calcite, or zeolites through hydrothermal activity.
Uses & applications
Primarily used as a decorative specimen for collectors; crushed basalt is used in construction and road base.
Geological facts
The white spots are called amygdules, derived from 'amygdala', the Latin word for almond. These rocks reflect a two-stage history: first an eruption, then mineral deposition from fluids.
Field identification & locations
Look for a dark or reddish dense matrix containing rounded, lighter-colored mineral 'pockets'. Commonly found in volcanic fields such as the Lake Superior region or the American Northwest.
