mineral

Tumbled smoky quartz or dark agate

Quartz, SiO₂; possibly chalcedony, microcrystalline SiO₂

AI-generated identification · may be incorrect

Smooth, polished, translucent-to-opaque brown-gray stone with vitreous/waxy luster; quartz hardness is 7 Mohs, no cleavage, conchoidal fracture, and specific gravity about 2.65. The image alone cannot distinguish smoky quartz from brown chalcedony or dyed agate confidently.

Identified September 21, 2026More mineral →

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Physical properties

Formation & geological history

Quartz and chalcedony form in silica-rich hydrothermal veins, cavities, and volcanic rocks; smoky coloration commonly results from radiation-induced defects, while agate develops as banded cavity fillings. Formation ages vary widely, from thousands to billions of years.

Uses & applications

Commonly sold as a tumbled lapidary stone, worry stone, decorative object, or jewelry component; not generally used as construction aggregate in this polished form.

Geological facts

A steel blade should not scratch quartz, while quartz can scratch ordinary glass. Strong translucence and conchoidal edges favor quartz or chalcedony; visible banding would indicate agate.

Field identification & locations

Common sources include Brazil, Madagascar, Uruguay, Mexico, and the United States. Check for dye concentration in cracks, glass-like luster, and hardness; laboratory testing or a close photograph is needed for exact identification.