sedimentary

Banded Chert (Agate)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

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 May 10, 2026More sedimentary →

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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.