igneous
Porphyritic basalt (likely vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and olivine
AI-generated identification · may be incorrectFine-grained, gray-green groundmass with scattered dark mafic crystals and small vesicles; dull to slightly vitreous luster, no obvious cleavage, hardness about 5–6, and specific gravity roughly 2.8–3.1.
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Physical properties
Fine-grained, gray-green groundmass with scattered dark mafic crystals and small vesicles; dull to slightly vitreous luster, no obvious cleavage, hardness about 5–6, and specific gravity roughly 2.8–3.1.
Formation & geological history
An extrusive igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions. Its exact geological age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, road stone, riprap, dimension stone, and landscaping material; attractive polished pieces are collected but generally have modest gem value.
Geological facts
The pale speckled appearance may reflect weathering or alteration of basalt, while the dark spots are likely pyroxene, olivine, or basaltic fragments. Rounded edges indicate transport or beach/river abrasion.
Field identification & locations
Identify it by its heavy feel, fine-grained texture, dark mafic minerals, and lack of visible quartz; it commonly occurs in volcanic regions, oceanic crust, and basalt-rich river or beach gravels. A hand lens and streak/magnet tests can help distinguish it from gabbro or slag.
