sedimentary

Banded Chert / Agate

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Dark grey to black with brownish-grey banding; Luster: Waxy to sub-vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Dark grey to black with brownish-grey banding
Luster: Waxy to sub-vitreous

Identified July 23, 2026More sedimentary →

Explore Banded Chert / Agate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in marine environment sediments through the deposition of microcrystalline silica, often precipitated from water or derived from biogenic silica like radiolarian tests, subsequently compressed and cemented over millions of years.

Uses & applications

Historically used for stone tools like arrowheads and scrapers due to conchoidal fracturing. Modern usage includes decorative lapidary work, tumbling, landscaping, and mineral collecting.

Geological facts

Banded cherts and jasper-agates are often stream-rounded or beach-worn into smooth pebbles. Their fine-grained structure makes them extremely durable and resistant to weathering.

Field identification & locations

Identify in the field by its distinct banding, hardness (scratches glass), waxy polish when water-worn, and sharp conchoidal fractures where broken. Commonly found in riverbeds, glacial tills, and coastal beaches.