mineral

Polished black stone, likely black agate or obsidian

Possible chalcedony (SiO₂) or volcanic glass (obsidian, SiO₂)

AI-generated identification · may be incorrect

Small, highly polished, opaque black specimen with vitreous-to-waxy luster and rounded/tumbled shape. Hardness is likely Mohs 5–7; crystal structure is cryptocrystalline for agate or amorphous for obsidian. The image lacks diagnostic banding or conchoidal fractures.

Identified September 17, 2026More mineral →

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Physical properties

Formation & geological history

Black agate forms when silica-rich fluids fill cavities in volcanic rock; obsidian forms by rapid cooling of silica-rich lava. Neither can be dated reliably from appearance alone. Both are plausible as transported or commercially tumbled material near 13.5°N, 77.5°E, though the photograph is insufficient for a precise identification.

Uses & applications

Used as a decorative stone, worry stone, bead, cabochon, or inexpensive jewelry material. Common tumbled pieces typically have modest value.

Geological facts

A strong flashlight may reveal translucence at thin edges in agate, while obsidian commonly shows glassy conchoidal fracture and may have a brown or gray sheen. Magnetism would suggest an iron-rich substitute rather than ordinary agate or obsidian.

Field identification & locations

Test cautiously: agate usually scratches glass and shows waxy edges; obsidian also scratches glass but looks more glassy and breaks sharply. A streak test, translucency check, and close inspection for banding are useful. Nearby Deccan-related volcanic rocks and quartz-rich gravels make silica stones regionally plausible.