sedimentary

Chert (Flint) with Glauconite

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Mohs hardness: 6.5-7. Color: Tan, brownish-grey center with green exterior spotting. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Tan, brownish-grey center with green exterior spotting
Luster: Waxy to vitreous

Identified February 21, 2026More sedimentary →

Explore Chert (Flint) with Glauconite in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Mohs hardness: 6.5-7. Color: Tan, brownish-grey center with green exterior spotting. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed in marine environment layers via chemical precipitation or replacement of carbonate minerals. The green spots are likely Glauconite, a common indicator of marine sedimentation.

Uses & applications

Historically used for stone tools and strike-a-lights. Currently used as an abrasive, in road construction, and for lapidary work (tumbled stones/jewelry).

Geological facts

Chert is so tough and chips with such sharp edges that it was the primary material for prehistoric arrowheads and spear points for thousands of years.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) breaking pattern. Found globally in limestone formations and as river cobbles.