sedimentary
Chert (specifically Brown Chert or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Dark brown to liver-colored; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Dark brown to liver-colored
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Dark brown to liver-colored; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.
Formation & geological history
Formed from the accumulation of microscopic silica-rich shells (radiolaria or diatoms) on the seafloor or via chemical replacement of carbonate materials. Occurs in sedimentary beds and as nodules within limestone or chalk.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as landscaping stone, in road construction (aggregate), and occasionally as a semi-precious gemstone (Jasper).
Geological facts
Chert has been used by humans for millions of years. When struck, it breaks with a conchoidal (shell-like) fracture, creating incredibly sharp edges that were essential for prehistoric survival.
Field identification & locations
Identify in the field by its smooth, waxy texture and curved, glass-like fracture surfaces. It commonly occurs as rounded nodules or distinct layers within sedimentary rock outcrops. It is harder than steel and will scratch a knife blade.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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