sedimentary
Banded Chert (Agate)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Brown, tan, and white banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 Mohs
- Color
- Brown, tan, and white banding
- Luster
- Waxy to vitreous
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 Mohs; Color: Brown, tan, and white banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed as a microcrystalline sedimentary rock from the precipitation of silica in groundwater or from the accumulation of silica-rich microfossils. These specimens often originate in marine environments or volcanic cavities.
Uses & applications
Used primarily for lapidary work, jewelry (beads and cabochons), and as landscaping stones. Historically used for making sharp tools like arrowheads due to its conchoidal fracture.
Geological facts
Banded chert is often transitionally related to agate. The distinct layers reflect changes in the chemistry of the silica-rich fluids during the accumulation or deposition process.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy appearance, and smooth, rounded surface when tumbled by water. Commonly found in riverbeds, glacial tills, and coastal beaches.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary