sedimentary
Chert (Jasper/Flint variety)
Sedimentary silica (SiO2)
Hardness: 7 on Mohs scale. Color: Brown, tan, and reddish-orange. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and reddish-orange
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Brown, tan, and reddish-orange. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich microfossils or through chemical precipitation from groundwaters in sedimentary environments such as limestone or shale beds.
Uses & applications
Historically used for stone tools and sparks; currently used in landscaping and as a collector specimen. Semi-precious varieties are used in jewelry.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be shaped into razor-sharp tools like arrowheads and knives.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy luster on fresh surfaces, and smooth, curved fracture edges. Commonly found in riverbeds and limestone outcrops.
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