sedimentary
Chert (varieties: Flint, Jasper)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 7 (Mohs scale); Color: Gray, tan, brown, or white; Luster: Waxy to dull; Breakage: Conchoidal fracture (curved surfaces); Structure: Cryptocrystalline; Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, brown, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, brown, or white; Luster: Waxy to dull; Breakage: Conchoidal fracture (curved surfaces); Structure: Cryptocrystalline; Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, knives) due to its sharp edges; used as flint for sparks; currently used in industrial abrasives and road construction.
Geological facts
Chert is so hard it can scratch steel. It is one of the most durable rocks on Earth, often surviving long after the surrounding limestone has eroded away. Flint is a specific dark variety of chert commonly found in chalk.
Field identification & locations
Identify in the field by its waxy texture and shell-like (conchoidal) fractures. It will not react with acid, unlike the limestone it is often found in. Common in gravel beds and mountain outcrops.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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