mineral

Tumbled agate/chalcedony pebble

Microcrystalline quartz (SiO₂), likely gray chalcedony with iron-oxide or other mineral inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; pale gray, blue-gray, and cream coloration; waxy to dull luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth rounded shape indicates tumbling or natural water wear.

Identified September 17, 2026More mineral →

Explore Tumbled agate/chalcedony pebble in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures, commonly in volcanic rocks, producing chalcedony and sometimes banded agate; most deposits are Cenozoic to older. The specimen may have been polished or naturally river-rounded.

Uses & applications

Used for beads, cabochons, carvings, paperweights, and decorative stone; attractive banding can increase jewelry value.

Geological facts

Chalcedony is quartz composed of microscopic interlocking crystals, so individual quartz crystals are usually invisible. Iron, manganese, and clay inclusions create much of its gray, cream, and brown color.

Field identification & locations

Identify by its glassy-to-waxy surface, quartz-like hardness, lack of cleavage, and conchoidal chips; it should scratch glass but not be scratched by a steel knife. Common in volcanic terrains and gravel deposits worldwide.