sedimentary
Chert (specifically Yellow Jasper/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Yellow, white, and grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Yellow, white, and grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellow, white, and grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. It typically occurs as nodules or layers in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads). Today used in jewelry as lapidary material, in landscaping, and as a low-cost gemstone for collectors.
Geological facts
Yellow chert gets its color from iron oxide (limonite) impurities. Because of its hardness and conchoidal fracture, it can create sharp edges when struck, a process known as flintknapping.
Field identification & locations
Identify in the field by its smooth, waxy feel and the way it breaks into curved, shell-like patterns (conchoidal fracture). It will not be scratched by a steel pocketknife. Commonly found in riverbeds and areas with exposed sedimentary rock.
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