sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and ochre due to iron oxides; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Red, brown, and ochre due to iron oxides
Luster: Dull to waxy

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and ochre due to iron oxides; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich fluids or organic remains (like radiolarians) in sedimentary environments. The red/brown coloration suggests high iron content (hematite/goethite staining).

Uses & applications

Historically used for stone tools due to its sharp edges. Modernly used for lapidary work, landscaping, and as a semi-precious gemstone in jewelry.

Geological facts

Chert is so durable that it can survive millions of years of erosion. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture patterns. Frequently found in riverbeds or as nodules within limestone layers.