sedimentary
Chert (and Fossiliferous Chert)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Cream, tan, and grey, Luster: Waxy to dull/earthy, Crystal structure: Microcrystalline (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Cream, tan, and grey, Luster: Waxy to dull/earthy, Crystal structure: Microcrystalline (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine environments during various geological eras from the Precambrian to the Cenezoic.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to conchoidal fracture. Currently used in construction aggregate and as a collector's specimen if fossilized.
Geological facts
Chert is a chemical sedimentary rock and is one of the most durable rocks on the planet. This specific piece appears to have darkened spots that may be remnants of internal fossil structures or mineral inclusions.
Field identification & locations
Identify in the field by its hardness (it scratches glass) and smooth, shell-like fracture surfaces. Often found in riverbeds, coastal beaches, and within limestone or dolostone layers.
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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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