igneous
Amygdaloidal Basalt
Extrusive mafic igneous rock with amygdules
Hardness of 6 on the Mohs scale, dark reddish-brown to grey color with lighter green or white secondary mineral infillings (amygdules), aphanitic to porphyritic texture, dull to sub-resinous luster, specific gravity around 2.8 to 3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark reddish-brown to grey color with lighter green or white secondary mineral infillings (amygdules), aphanitic to porphyritic texture, dull to sub-resinous luster, specific gravity around 2.8 to 3.0.
Formation & geological history
Formed from cooling basaltic lava flows where gas bubbles (vesicles) were later filled with secondary minerals such as quartz, calcite, or zeolites through hydrothermal or groundwater activity.
Uses & applications
Used in landscaping, road construction, aggregate, and by mineral collectors interested in the secondary minerals found within the vesicles.
Geological facts
Amygdules often contain precious minerals such as agates, zeolites, or native copper, making them particularly exciting finds for rockhounds in regions like the Lake Superior basin.
Field identification & locations
Easily identified by its dark, fine-grained matrix punctuated by distinct rounded or elongated spots (amygdules) of contrasting mineral infill. Commonly found in ancient volcanic provinces and flood basalt regions.
