sedimentary
Chert
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: Gray to light blue with mottled patterns, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6
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Physical properties
Hardness: 7 (Mohs scale), Color: Gray to light blue with mottled patterns, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation within limestone/chalk beds. Primarily Paleozoic to Mesozoic era formation.
Uses & applications
Used historically for stone tools due to its sharp edges; currently used in construction aggregate, road base, and as decorative river stones.
Geological facts
Chert is so durable that it often remains behind as 'lag' after the surrounding limestone has weathered away. Known as flint when found in chalk.
Field identification & locations
Identify by its hardness (scratches glass), smooth waxy texture, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or within sedimentary limestone outcrops.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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