sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brown, white, Luster: waxy to dull, Fracture: conchoidal, Structure: microcrystalline quartz
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brown, white, Luster: waxy to dull, Fracture: conchoidal, Structure: microcrystalline quartz
Formation & geological history
Formed in sedimentary environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone or dolostone. Dates back to various geological eras.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used as road aggregate, architectural stone, and occasionally for lapidary work.
Geological facts
Chert is so hard it can strike sparks against steel. It is chemically identical to quartz but has a much finer, denser crystal structure.
Field identification & locations
Identify by its waxy texture, hardness (it scratches glass), and smooth, shell-like (conchoidal) breaks. Extremely common in gravel and riverbeds globally.
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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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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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