sedimentary
Chert (Golden/Yellow Variety)
Microcrystalline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: Yellow, tan, amber, and brown; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Yellow, tan, amber, and brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellow, tan, amber, and brown; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) in deep-sea environments. Often found in nodules within limestone or dolostone strata ranging from Precambrian to Cenozoic ages.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, architectural stone, and occasionally tumbled for jewelry or lapidary art.
Geological facts
Chert is chemically identical to quartz but has a different internal structure. Because of its extreme hardness and durability, it was one of the most important minerals for early human technological development, used to start fires and create weapons.
Field identification & locations
Identify in the field by its distinctive conchoidal (shell-like) fracture, waxy feel, and inability to be scratched by a steel pocketknife. Common in the Midwest USA, the UK, and ancient seafloor deposits worldwide.
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