igneous
Amygdaloidal Basalt
Amygdaloidal Basalt (mafic extrusive rock with secondary mineral infillings)
AI-generated identification · may be incorrectHardness 5.5–6.5 (Mohs), dark grey-black aphanitic groundmass with dull to earthy luster, embedded with rounded, pale mineral-filled gas vesicles (amygdules), specific gravity 2.8–3.0.
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Physical properties
Hardness 5.5–6.5 (Mohs), dark grey-black aphanitic groundmass with dull to earthy luster, embedded with rounded, pale mineral-filled gas vesicles (amygdules), specific gravity 2.8–3.0.
Formation & geological history
Forms from the cooling of gas-rich mafic lava where escaping vesicles later fill with secondary hydrothermal minerals such as calcite, quartz, or zeolites.
Uses & applications
Commonly crushed for construction aggregate, road base, and railroad ballast, with unique specimens collected by mineral enthusiasts.
Geological facts
The pale inclusions were originally gas bubbles trapped inside cooling volcanic lava that were later crystallized by percolating groundwater.
Field identification & locations
Identify by a dark, fine-grained matrix hosting contrasting pale, rounded mineral fillings. Found in regional basaltic flows and metamorphic belts across North Carolina's Piedmont.
