sedimentary
Chert (Chalcedony/Agate)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brownish-yellow, tan, and translucent white; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 6
- Color
- Brownish-yellow, tan, and translucent white
- Luster
- Waxy to vitreous
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: Brownish-yellow, tan, and translucent white; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed via the precipitation of silica from groundwater or within sedimentary rock layers like limestone. This specimen appears water-worn, likely tumbled in a river or coastal environment over thousands of years.
Uses & applications
Historically used for making stone tools; currently used for decorative stone, lapidary work, jewelry (when polished), and aggregate in construction.
Geological facts
This specific sample shows clear waxy luster and translucency typical of chalcedony. Chert is so durable that it often survives long after the surrounding rock has eroded away.
Field identification & locations
Identified by its waxy texture, lack of visible crystals, and conchoidal (shell-like) fracture patterns. Found globally in gravel beds, beaches, and sedimentary basins.
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