sedimentary
Chert (Jasper/Agate variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brownish, reddish-pink, Luster: waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brownish, reddish-pink, Luster: waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils on the seafloor or by the replacement of carbonate minerals by silica in groundwater. This process can occur over millions of years.
Uses & applications
Historically used for stone tools (knapping). Currently used as decorative landscaping rock, jewelry (when polished), and as a gemstone for collectors.
Geological facts
Chert was one of the first resources humans traded over long distances. Because it breaks with a conchoidal fracture like glass, it creates edges sharper than a steel scalpel.
Field identification & locations
Identify by its 'bottleglass' fracture pattern, smooth waxy texture on broken surfaces, and extreme hardness (it will scratch glass). Commonly found in limestone or dolomite deposits.
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