igneous
Likely tumbled black basalt or volcanic glass
Basalt (plagioclase–pyroxene rock), possibly obsidian (volcanic glass)
AI-generated identification · may be incorrectDark black, glossy surface with irregular conchoidal-looking edges; hardness approximately 5–6 for basalt or 5–5.5 for obsidian, with no visible crystals or cleavage. The strong shine may result from polishing or a naturally glassy surface.
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Physical properties
Dark black, glossy surface with irregular conchoidal-looking edges; hardness approximately 5–6 for basalt or 5–5.5 for obsidian, with no visible crystals or cleavage. The strong shine may result from polishing or a naturally glassy surface.
Formation & geological history
An igneous specimen formed from rapidly cooled mafic lava; basalt crystallizes as lava cools, whereas obsidian forms when silica-rich lava quenches into glass. Such rocks are geologically young to ancient and occur in volcanic terrains worldwide.
Uses & applications
Used as aggregate, paving stone, landscaping material, and occasionally as a decorative or lapidary specimen; obsidian is also used for carvings and jewelry.
Geological facts
The image alone cannot reliably distinguish basalt from obsidian, especially because the specimen appears polished or wet. A streak, close inspection for tiny crystals, and examination of fracture surfaces would help.
Field identification & locations
Common in volcanic regions, including Iceland, Hawaii, Mexico, the western United States, and East Africa. Basalt feels dense and granular; obsidian has glassy conchoidal fractures and typically leaves a white-to-gray streak.
