igneous
Small dark tumbled stone (likely basalt or iron-rich mineral)
Uncertain; possibly basalt (fine-grained plagioclase–pyroxene rock) or magnetite-rich material (Fe₃O₄)
AI-generated identification · may be incorrectDark black-brown, opaque, rounded and polished, with subdued vitreous-to-waxy luster; apparent size is roughly 2 cm. Hardness and specific gravity cannot be determined reliably from the image; magnetite would be Mohs 5.5–6.5 and strongly magnetic, while basalt is about 6.
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Physical properties
Dark black-brown, opaque, rounded and polished, with subdued vitreous-to-waxy luster; apparent size is roughly 2 cm. Hardness and specific gravity cannot be determined reliably from the image; magnetite would be Mohs 5.5–6.5 and strongly magnetic, while basalt is about 6.
Formation & geological history
If basalt, it formed from rapidly cooled volcanic lava, generally in relatively young volcanic terrains; if magnetite-rich, it may be an accessory mineral in igneous or metamorphic rocks. The smooth shape indicates natural abrasion or tumbling.
Uses & applications
Common basalt has little commercial value as a small specimen, though basalt is widely used as crushed aggregate and building stone; magnetite is an important iron ore. Typical value is about $1–$10 for a small common tumbled specimen.
Geological facts
The image is too blurred for definitive identification. A magnet test, streak test, and close inspection of texture would distinguish magnetite from basalt and other dark stones.
Field identification & locations
Check for attraction to a strong magnet, a black streak on unglazed porcelain, visible tiny crystals, and density; avoid destructive testing if collectible. Dark tumbled stones are commonly sold from volcanic regions and lapidary suppliers.
