sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids. This specimen appears to be a nodule or fragment found within gravel deposits.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; currently used for decorative stones, landscaping, and as a source of silica in glass manufacturing.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create arrowheads, scrapers, and knives because it breaks with a predictable, razor-sharp conchoidal fracture.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy appearance on freshly broken surfaces, and shell-like (conchoidal) fracture pattern. Often found in riverbeds or as nodules in limestone.
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