sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark brown/black (common in iron-rich areas), Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark brown/black (common in iron-rich areas), Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians) or the chemical precipitation of silica in groundwater. Can be found in geological formations ranging from the Precambrian to the present.
Uses & applications
Historically used for making stone tools (arrowheads). Today used as aquarium gravel, in landscaping, or as tumbled stones for hobbyists.
Geological facts
Chert is so durable that it can survive long-distance transport in rivers, leading to the rounded, 'pebble' shape seen in this specimen. It produces sparks when struck against steel.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and glacial deposits.
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