igneous
Polished black stone, likely basalt or amphibolite
Basalt (fine-grained mafic rock), possibly amphibolite; primarily plagioclase and pyroxene/amphibole
AI-generated identification · may be incorrectDark gray-black, elongated and highly polished with a fine-grained texture and subtle pale mineral streaks; likely Mohs hardness 5–6, opaque, with a vitreous-to-waxy surface after polishing. Exact identification requires an unpolished surface or testing.
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Physical properties
Dark gray-black, elongated and highly polished with a fine-grained texture and subtle pale mineral streaks; likely Mohs hardness 5–6, opaque, with a vitreous-to-waxy surface after polishing. Exact identification requires an unpolished surface or testing.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly in oceanic crust and volcanic fields; if amphibolite, it is metamorphosed basalt formed under elevated temperature and pressure. Geological age is indeterminate from the image.
Uses & applications
Used as decorative stone, lapidary material, massage/hand stones, aggregate, and occasionally architectural stone; typically modest collector value.
Geological facts
The smooth elongated form appears deliberately shaped and polished rather than naturally weathered. Pale flecks may represent feldspar, quartz, or altered amphibole.
Field identification & locations
Check for visible crystals, magnetic response, streak, and density; basalt is usually fine-grained and dense, while amphibolite commonly shows aligned amphibole grains. Common sources include volcanic and metamorphic terrains worldwide.
