sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness: 7 on the Mohs scale, Color: Yellowish, tan, brown, or white, Luster: Waxy to dull, Crystal structure: Microcrystalline/cryptocrystalline (quartz), Cleavage: None (exhibits conchoidal fracture), Specific Gravity: 2.60 - 2.65
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Physical properties
Hardness: 7 on the Mohs scale, Color: Yellowish, tan, brown, or white, Luster: Waxy to dull, Crystal structure: Microcrystalline/cryptocrystalline (quartz), Cleavage: None (exhibits conchoidal fracture), Specific Gravity: 2.60 - 2.65
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of marine organisms (like radiolarians or diatoms) in marine environments over millions of years.
Uses & applications
Historically used by early humans for making stone tools, arrowheads, and blades due to its conchoidal fracture; occasionally used for decorative landscaping or tumbling.
Geological facts
Chert forms nodules or layers within sedimentary rocks such as limestone and chalk. Varieties include flint, jasper, and chalcedony depending on color and impurities.
Field identification & locations
Can be identified in the field by its hardness (scratches glass), waxy luster, and smooth conchoidal fracture edges. Commonly found in limestone and river gravels worldwide.
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