igneous
Amygdaloidal basalt pebble
Vesicular basalt, locally calcite- or quartz-filled amygdales
AI-generated identification · may be incorrectDark gray, fine-grained mafic rock with pale rounded vesicles and white mineral veins; typically dull to faintly satin luster, hardness about 5–6, massive texture, and no cleavage. The white fillings are likely calcite, quartz, or zeolite minerals.
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Physical properties
Dark gray, fine-grained mafic rock with pale rounded vesicles and white mineral veins; typically dull to faintly satin luster, hardness about 5–6, massive texture, and no cleavage. The white fillings are likely calcite, quartz, or zeolite minerals.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles later filled by groundwater minerals. Its exact age is indeterminate from the image; such basalt occurs from Precambrian to modern volcanic settings.
Uses & applications
Commonly used as aggregate, road stone, landscaping material, and decorative pebble; attractive specimens may be collected but are generally low-value.
Geological facts
The rounded cavities are called amygdales, distinguishing amygdaloidal basalt from ordinary dense basalt. White vein material may indicate later hydrothermal or weathering activity.
Field identification & locations
Identify it by its dark fine-grained groundmass, light-filled cavities, and occasional pale veins; a streak test, hardness test, and acid test can help distinguish calcite from quartz. Common worldwide in volcanic regions, river gravels, and glacial deposits.
