sedimentary
Chert Concretion / Nodule
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, yellowish-brown; Luster: Waxy to dull; Texture: Cryptocrystalline, smooth conchoidal fracture; Cleavage: None
- Hardness
- 6
- Color
- Tan, beige, yellowish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, yellowish-brown; Luster: Waxy to dull; Texture: Cryptocrystalline, smooth conchoidal fracture; Cleavage: None
Formation & geological history
Formed by the chemical precipitation of silica within sedimentary rock layers, often limestone or chalk. Many originate from the accumulation of silica-rich organic remains like sponges or diatoms. Age varies significantly by deposit floor.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to conchoidal fracture. Currently used in road construction, landscaping, and as a collector specimen.
Geological facts
Chert nodules are often mistaken for fossils because of their rounded, organic shapes. In some regions, they are referred to as 'flint' if found in chalk.
Field identification & locations
Identify in the field by its hardness (will scratch steel) and its smooth, shell-like fracture pattern when broken. Commonly found in riverbeds or eroding out of limestone cliffs.
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