sedimentary
River Agate (Chert/Chalcedony)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs). Color: Variegated greens, grays, and whites. Luster: Waxy to vitreous when wet. Crystal structure: Microcrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Variegated greens, grays, and whites
- Luster
- Waxy to vitreous when wet
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 (Mohs). Color: Variegated greens, grays, and whites. Luster: Waxy to vitreous when wet. Crystal structure: Microcrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the deposition of silica from groundwater in cavities of igneous rocks or sedimentary layers. These specimens were smoothed and rounded over millions of years by river transport and abrasive action.
Uses & applications
Used primarily for lapidary work, jewelry making (cabochons), and as decorative landscape stone or in rock tumbling.
Geological facts
River rocks like these are natural 'tumblers'—the moving water and friction against other rocks acts exactly like a mechanical rock tumbler, creating smooth surfaces over centuries.
Field identification & locations
Identify in the field by its smoothness, slight translucency at the edges when held to light, and its resistance to scratching with a steel knife. Commonly found in riverbeds and gravel pits.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary