sedimentary
Chert
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: White to tan with slight weathering, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: White to tan with slight weathering, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich microfossils or inorganic precipitation in marine or groundwater environments. It typically forms within limestone or chalk beds as nodules or layers.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include road surfacing materials, decorative landscaping, and as a raw material for ceramics and glass.
Geological facts
Chert is so hard it can strike sparks against steel. It was one of the most important minerals for prehistoric humans because it breaks into very sharp edges through conchoidal fracturing.
Field identification & locations
Identify by its high hardness (cannot be scratched by a steel knife), dull appearance, and smooth, shell-like (conchoidal) breaks. It is commonly found in sedimentary basins and riverbeds.
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Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
fossil
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite
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Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary