mineral
Agate (Water-Worn Pebble)
Silicon Dioxide (SiO2) - Chalcedony
AI-generated identification · may be incorrectHardness: 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)
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Physical properties
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.
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.
