sedimentary
Chert (or Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan to brown with white patches, Luster: waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to brown with white patches, Luster: waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed primarily through the precipitation of silica from groundwater in sedimentary environments, often replacing organic material or filling cavities in limestone or dolostone.
Uses & applications
Historically used for making stone tools; currently used in construction as aggregate, for lapidary work, and as aquarium gravel.
Geological facts
Chert is so hard it can strike sparks against steel. Examples like flint have been used by humans for hundreds of thousands of years to create fire and sharp tools.
Field identification & locations
Identify in the field by its waxy luster and smooth, curved (conchoidal) fracture surfaces. Commonly found in riverbeds and limestone outcrops.
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