igneous
Quartz-lined vesicle in basalt (amygdaloidal basalt)
Amygdaloidal basalt with drusy quartz; predominantly plagioclase, pyroxene, and iron oxides
AI-generated identification · may be incorrectHardness is about 6–7 overall (quartz 7); dark, fine-grained volcanic matrix with a rusty-brown weathering surface and white to gray sparkling quartz crystals. Quartz has vitreous luster and conchoidal fracture; the basalt is typically massive with no obvious cleavage.
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Physical properties
Hardness is about 6–7 overall (quartz 7); dark, fine-grained volcanic matrix with a rusty-brown weathering surface and white to gray sparkling quartz crystals. Quartz has vitreous luster and conchoidal fracture; the basalt is typically massive with no obvious cleavage.
Formation & geological history
Formed when gas bubbles in cooling basaltic lava later filled with silica-rich fluids, crystallizing quartz in the vesicle. The basalt is commonly Cenozoic or older, depending on its volcanic setting.
Uses & applications
Primarily a collector specimen or decorative stone; quartz-lined cavities may be cut or displayed, but this material has little industrial value.
Geological facts
The cavity is a geode-like vesicle, and the crystals appear drusy—many small crystals coating the interior rather than one large crystal.
Field identification & locations
Identify it by the dark volcanic host, rounded cavity, and glassy quartz coating; acid testing should not fizz. Common in basaltic volcanic provinces worldwide, including the western United States, Iceland, India, and Scotland.
