sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Mohs hardness 7, dark brown to grey earthy color, dull to sub-vitreous luster, microcrystalline/cryptocrystalline structure, conchoidal fracture, specific gravity ~2.65
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Physical properties
Mohs hardness 7, dark brown to grey earthy color, dull to sub-vitreous luster, microcrystalline/cryptocrystalline structure, conchoidal fracture, specific gravity ~2.65
Formation & geological history
Formed via chemical precipitations or biochemical accumulation of siliceous oozes in deep marine or lake environments, often replacing carbonates during diagenesis.
Uses & applications
Historically used for stone tools, arrowheads, and spark-striking flintlocks. Modernly used as road aggregate and ornamental stones.
Geological facts
Chert was one of the earliest raw materials utilized by prehistoric humans due to its ability to break into sharp, knife-like edges with conchoidal fractures.
Field identification & locations
Can be identified in the field by its high hardness (scratches glass), waxy to dull luster, smooth conchoidal fracture edges, and lack of reaction to dilute hydrochloric acid.
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