mineral
Tumbled brown-black stone, likely smoky quartz or iron-stained agate
Indeterminate from image; possible quartz (SiO₂), chalcedony, or iron-rich jasper
AI-generated identification · may be incorrectDark brown to black, smoothly tumbled, with subdued vitreous-to-waxy luster and lighter brown internal bands or staining. Quartz-group material has Mohs hardness about 7, no obvious cleavage, and conchoidal fracture; exact identification requires testing.
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Physical properties
Dark brown to black, smoothly tumbled, with subdued vitreous-to-waxy luster and lighter brown internal bands or staining. Quartz-group material has Mohs hardness about 7, no obvious cleavage, and conchoidal fracture; exact identification requires testing.
Formation & geological history
Likely natural silica deposited in volcanic cavities or fractures, later colored by iron oxides and rounded by tumbling. The geological age cannot be determined visually and depends on its source deposit.
Uses & applications
Used mainly as a lapidary, craft, or collectible stone; quartz varieties may be cut into cabochons or beads. It has little value unless it displays attractive banding, translucency, or a recognized locality.
Geological facts
The image may show a small polished mineral specimen rather than a distinct rock type. Stronger identification would require a streak test, hardness test, translucency check, and examination of the unpolished surface.
Field identification & locations
Commonly encountered in mixed tumbled-stone assortments from Brazil, Madagascar, India, or the United States. Quartz should scratch glass but not be scratched by a steel knife; avoid testing valuable material.
