sedimentary
Chert
Chert (SiO2, Silicon Dioxide)
Hardness: 6.5-7 Mohs. Color: Gray, tan, or brown. Luster: Waxy to dull. Structure: Microcrystalline/cryptocrystalline quartz. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Gray, tan, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs. Color: Gray, tan, or brown. Luster: Waxy to dull. Structure: Microcrystalline/cryptocrystalline quartz. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed in marine environments through the accumulation of siliceous organisms or chemical precipitation. Many specimens date from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road surfacing and as a raw material for silicon-based products. Often collected as river stones.
Geological facts
Chert is so hard it can create sparks when struck against steel. It is chemically similar to flint, but 'flint' usually refers specifically to dark nodules found in chalk.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy texture when wet, and curved, shell-like (conchoidal) fractures. Found worldwide in riverbeds and limestone 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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