igneous
Tumbled black stone, likely basalt or obsidian
Uncertain; likely fine-grained basalt (plagioclase–pyroxene) or dark volcanic glass (obsidian)
AI-generated identification · may be incorrectDark gray-black, glossy to waxy surface, rounded by tumbling, with no visible crystals; basalt is typically Mohs 5–6, while obsidian is about 5–5.5 and has conchoidal fracture. The bright metallic-looking flecks may be pyroxene, magnetite, or surface reflections.
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Physical properties
Dark gray-black, glossy to waxy surface, rounded by tumbling, with no visible crystals; basalt is typically Mohs 5–6, while obsidian is about 5–5.5 and has conchoidal fracture. The bright metallic-looking flecks may be pyroxene, magnetite, or surface reflections.
Formation & geological history
Volcanic igneous material formed from rapidly cooled lava; basalt crystallizes relatively quickly, whereas obsidian cools so fast that crystals do not form. Such pieces commonly originate from relatively young volcanic terrains, though volcanic rocks can be geologically ancient.
Uses & applications
Used as landscaping aggregate, road stone, and lapidary material; attractive polished pieces may be sold as pocket stones or cabochons. This small tumbled specimen has modest commercial value.
Geological facts
Basalt is the most abundant volcanic rock on Earth, forming much of oceanic crust. Obsidian can produce exceptionally sharp conchoidal edges, historically used for cutting tools.
Field identification & locations
Check for tiny interlocking crystals and a duller, heavier texture to support basalt; uniformly glassy texture and curved shell-like breaks suggest obsidian. Common sources include volcanic regions such as Hawaii, Iceland, Mexico, and the western United States.
