mineral

Tumbled chalcedony pebble

Chalcedony, microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, and honey-brown coloration with a waxy to vitreous luster. It has cryptocrystalline quartz structure, no visible cleavage, and specific gravity about 2.58–2.64.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic and sedimentary rocks; coloration commonly comes from iron oxides. The rounded, smooth surface indicates natural water abrasion or human tumbling, not a distinct geological age.

Uses & applications

Used for beads, cabochons, carvings, ornamental objects, and inexpensive collector specimens; larger patterned varieties are valued as agate or jasper.

Geological facts

Chalcedony is an aggregate of extremely tiny quartz crystals, so individual crystals are generally invisible. Brown or yellow zones commonly reflect limonite or hematite impurities.

Field identification & locations

Identify it by its smooth waxy appearance, translucent edges, quartz hardness, and lack of cleavage; it should scratch ordinary glass but not be scratched by a steel knife. Common worldwide, including volcanic terrains and alluvial gravels.