sedimentary
Chert Nodules in Sedimentary Rock
Microcrystalline Quartz (SiO2) within Clastic Matrix
Hardness: 6.5-7. Color: Tan, brownish-gray, and cream. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, brownish-gray, and cream
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7. Color: Tan, brownish-gray, and cream. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed via the precipitation of silica within marine or lacustrine sediment layers, often replacing organic material or filling voids in existing sedimentary rock over millions of years.
Uses & applications
Historically used for stone tools due to conchoidal fracturing; used today as decorative garden stones, river rock for landscaping, or road aggregate.
Geological facts
Chert is so durable that it often survives the weathering of its host limestone or dolomite, resulting in smooth, rounded nodules found in riverbeds like this one.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, water-worn texture compared to softer surrounding rocks. Commonly found in riverbeds and gravel pits.
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