sedimentary
Chert (variously known as Flint or Microcrystalline Quartz)
Silicon dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or off-white with iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the replacement of carbonate minerals in limestone/chalk. Found in formations ranging from Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; currently used as construction aggregate, road base, and occasionally in lapidary work.
Geological facts
Chert has a unique breaking pattern called conchoidal fracture, which results in smooth, curved surfaces similar to glass. It was one of the most vital materials for stone-age technology.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), its waxy feel, and its curved, shell-like fracture marks. Commonly found as nodules or layers within limestone beds.
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