sedimentary
Chert (Yellow Jasper/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7.0 (Mohs scale); Color: Yellow-brown, olive, tan; Luster: Waxy to dull (glassy when wet); Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Yellow-brown, olive, tan
- Luster
- Waxy to dull (glassy when wet)
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Physical properties
Hardness: 6.5-7.0 (Mohs scale); Color: Yellow-brown, olive, tan; Luster: Waxy to dull (glassy when wet); Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the precipitation of silica from groundwater or within sedimentary basins. Often found as nodules in limestone or chalk beds. It can be millions of years old, originating from the Paleozoic to Cenozoic eras.
Uses & applications
Historically used for stone tools and fire-starting (flint). Currently used in landscaping, as tumbling rough for lapidary work, and for decorative gravel.
Geological facts
Chert is so hard that it can scratch steel. When broken, it produces sharp, curved edges called conchoidal fractures, which made it the primary material for prehistoric arrowheads.
Field identification & locations
Identify in the field by its smooth, waxy texture and sharp, shell-like edges where broken. It will not be scratched by a steel knife. Commonly found in riverbeds or coastal erosion zones.
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