sedimentary
Chert (often called Flint)
Chert (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, white, buff with iron staining, Luster: dull to waxy, Structure: microcrystalline quartz, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, white, buff with iron staining, Luster: dull to waxy, Structure: microcrystalline quartz, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone/chalk beds; often found as nodules or bedded deposits.
Uses & applications
Historical tool making (arrowheads/knives), construction aggregate, road stone, and occasionally used as a strike-stone for fire-starting.
Geological facts
Chert breaks with a conchoidal fracture, creating extremely sharp edges that were essential to prehistoric tool technology. It is chemically identical to quartz but has a different microscopic structure.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth waxy feel, and the distinctive curved, shell-like sharp fractures where it has been chipped.
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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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