sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brown, and yellowish-orange due to iron oxides, 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, brown, and yellowish-orange due to iron oxides, Luster: waxy to dull, Crystal Structure: trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. The iron staining (limonite/hematite) suggests secondary groundwater interaction and weathering.
Uses & applications
Historically used for stone tools and weapons due to its sharp conchoidal fracture. Modern uses include landscaping, road base, and occasionally as semi-precious gemstones (jasper) in jewelry.
Geological facts
Chert is so hard it can scratch steel and glass. It was used by ancient civilizations to start fires by striking it against steel to create sparks, a property shared with its variety, flint.
Field identification & locations
Identify by its waxy luster, jagged/curved (conchoidal) breaking pattern, and extreme hardness. Often found in riverbeds or within limestone and chalk deposits.
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