sedimentary
Chert (often called Flint when found in chalk)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brown, or greenish-yellow with waxy luster. Microcrystalline structure with conchoidal (shell-like) fracture. Generally opaque to translucent.
- Color
- tan, brown, or greenish-yellow with waxy luster
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brown, or greenish-yellow with waxy luster. Microcrystalline structure with conchoidal (shell-like) fracture. Generally opaque to translucent.
Formation & geological history
Formed through the precipitation of silica in sedimentary environments, often replacing organic material or filling cavities in carbonate rocks. Can be millions of years old, often from the Cretaceous period.
Uses & applications
Historically used for stone tools and strike-a-lights. Currently used in road surfacing, decorative landscaping, and occasionally as a gemstone in tumbled form.
Geological facts
Because of its hardness and the way it fractures into sharp edges, it was the primary material for spearheads and arrowheads during the Stone Age.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy feel, and smooth curved fracture surfaces. Commonly found in gravel beds, riverbanks, and coastal regions with chalk deposits.
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