sedimentary
Chert / Flint
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale; conchoidal fracture; colors range from gray, white, brown, to black; waxy to vitreous luster; cryptocrystalline structure with no visible crystal faces.
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Physical properties
Hardness of 7 on the Mohs scale; conchoidal fracture; colors range from gray, white, brown, to black; waxy to vitreous luster; cryptocrystalline structure with no visible crystal faces.
Formation & geological history
Forms in marine environments through the replacement of calcium carbonate sediments by silica-rich solutions or the accumulation of siliceous skeletal remains of microorganisms like diatoms and radiolarians.
Uses & applications
Historically used for making stone tools, arrowheads, and striking fire; currently used in abrasives, aggregate, and occasionally ornamental items.
Geological facts
Chert and flint are chemically identical forms of microcrystalline quartz, traditionally distinguished by color where darker varieties are often called flint.
Field identification & locations
Easily identified by its characteristic conchoidal fracture and high hardness (scratches glass). Commonly found in limestone and chalk formations worldwide.
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