igneous
Dark glassy pebble, possibly volcanic rock
Likely basalt or volcanic glass (var. obsidian), unconfirmed from image
AI-generated identification · may be incorrectSmall dark gray-black, irregular pebble with a dull to slightly vitreous luster; likely hardness about 5–6 (basalt) or 5–5.5 (obsidian). The surrounding surface appears to be concrete, but the object itself may be natural stone.
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Physical properties
Small dark gray-black, irregular pebble with a dull to slightly vitreous luster; likely hardness about 5–6 (basalt) or 5–5.5 (obsidian). The surrounding surface appears to be concrete, but the object itself may be natural stone.
Formation & geological history
Basalt forms from rapidly cooled mafic lava; obsidian forms when silica-rich lava cools so quickly that crystals do not develop, generally in volcanic settings younger than a few million years. Exact identification requires a close-up and testing.
Uses & applications
Common basalt is used for aggregate, road construction, and landscaping; obsidian is used for ornaments, tools, and jewelry. This small specimen has negligible commercial value.
Geological facts
Basalt is typically fine-grained and magnetic, whereas obsidian breaks with sharp, curved conchoidal fractures and commonly has a glassy sheen. The image resolution is insufficient to distinguish them confidently.
Field identification & locations
Check for visible crystals, a streak, magnetism, and conchoidal fracture; a fresh broken surface and hand lens are useful. Likely sources include volcanic terrains or imported landscaping aggregate.
