sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs). Color: Grey-blue with yellowish-brown veining. Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.65.
- Hardness
- 6
- Color
- Grey-blue with yellowish-brown veining
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Grey-blue with yellowish-brown veining. Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.65.
Formation & geological history
Formed from the precipitation of silica-rich fluids or the accumulation of siliceous organisms (like radiolaria or diatoms) in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Used historically for stone tools due to its sharp edges when fractured. Currently used for lapidary work, decorative landscaping, and as a component in construction aggregate.
Geological facts
Chert is one of the most durable sedimentary rocks. Because of its hardness and conchoidal fracture, it was the primary material used by prehistoric humans to create arrowheads, spear points, and scrapers.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fracture patterns. It can easily scratch glass and produces sparks when struck against steel. Found in riverbeds and sedimentary basins worldwide.
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