sedimentary
Chert Pebble
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, or brownish-grey; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, or brownish-grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, or brownish-grey; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed as a chemical precipitate or through the replacement of limestone by silica-rich fluids. Usually found in sedimentary layers or recycled as rounded pebbles in fluvial/glacial deposits.
Uses & applications
Historically used for stone tools (flint); currently used as construction aggregate, road base, and occasionally as decorative landscaping stone.
Geological facts
Chert is so hard it can scratch glass and steel. It is chemically identical to quartz but contains many microscopic impurities that make it opaque.
Field identification & locations
Identified by its extreme hardness, smooth texture, and curved, shell-like (conchoidal) fracture when broken. Found globally in riverbeds and coastal areas.
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