sedimentary
Chert (Chalcedony/Quartz)
Microcrystalline Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65
- Hardness
- 6
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed through the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms (diatoms/radiolarians) within sedimentary layers. This process creates dense, hard nodules or beds over millions of years.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, in landscaping, and as a collector's specimen.
Geological facts
Chert is essentially a variety of quartz that features such tiny crystals that they cannot be seen under a standard microscope. Flint is a well-known dark variety of chert.
Field identification & locations
Identified in the field by its hardness (scratches glass), waxy luster on fresh surfaces, and distinctive shell-like (conchoidal) fracture patterns when broken. Common in limestone and chalk formations worldwide.
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