igneous
Tumbled dark stone, possibly basalt or iron-rich chert
Indeterminate; likely fine-grained basalt (plagioclase–pyroxene) or ferruginous chert
AI-generated identification · may be incorrectDark brown-black, rounded and polished, with a vitreous-to-waxy luster and small lighter inclusions; hardness is approximately 5.5–7 Mohs, depending on composition. No cleavage is visible; specific gravity is roughly 2.6–3.0.
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Physical properties
Dark brown-black, rounded and polished, with a vitreous-to-waxy luster and small lighter inclusions; hardness is approximately 5.5–7 Mohs, depending on composition. No cleavage is visible; specific gravity is roughly 2.6–3.0.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly in oceanic or volcanic settings; if chert, it formed from microcrystalline silica in sedimentary environments. The specimen’s geological age cannot be determined from the photograph.
Uses & applications
Likely a tumbled lapidary or decorative stone, suitable for crafts, display, and informal collecting; it has little industrial or jewelry value without confirmed composition.
Geological facts
The smooth triangular form and glossy surface indicate mechanical tumbling or water abrasion. The pale specks may be weathered mineral grains, vesicles, or surface residue.
Field identification & locations
Test with a steel knife: basalt may scratch or be scratched near hardness 5–6, while chert should resist scratching; a streak, magnetism, and specific gravity test would help distinguish them. Common source regions include volcanic terrains and gravel deposits.
