sedimentary
Chert (Flint) with Glauconite
Microcrystalline Quartz (SiO2)
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
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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.
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