sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to green-grey, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to green-grey, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formation occurs as a chemical precipitate in marine or freshwater environments, often replacing calcium carbonate in limestone or forming from silica-rich organic remains.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers). Currently used in road construction, as an abrasive, and occasionally for lapidary work.
Geological facts
Chert is essentially the same mineral as flint and jasper; flint usually refers to varieties found in chalk/limestone, while jasper is iron-stained.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like conchoidal fracture patterns. Commonly found in stream beds and limestone outcrops.
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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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