mineral

Agate (Water-Worn Pebble)

Silicon Dioxide (SiO2) - Chalcedony

Hardness: 6.5-7 (Mohs). Color: Translucent grey with faint banding. Luster: Waxy to dull (frosted). Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Translucent grey with faint banding
Luster: Waxy to dull (frosted)

Identified April 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary deposit in volcanic cavities (gas bubbles) or sedimentary rocks. Over time, silica-rich water fills these voids, crystallizing in concentric layers. This specific specimen has been tumbled by water in a river or beach environment, giving it its rounded, frosted appearance.

Uses & applications

Used for semiprecious jewelry, decorative stones, lapidary arts, and historically for burnishing tools or mortars and pestles due to its hardness.

Geological facts

Agate is a variety of chalcedony characterized by its banding. The banding is caused by periodic changes in the composition of the mineral-bearing fluids during formation. This specimen shows 'ghost' or faint banding typical of many common beach agates.

Field identification & locations

Identify in the field by checking for translucency (light passing through), a waxy texture when wet, and the presence of fine, concentric banding. Commonly found in riverbeds, gravel pits, and along ocean coastlines where volcanic activity once occurred.

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