sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale, Color: Varies widely including brown, grey, white, and black, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/cryptocrystalline quartz, Cleavage: None (exhibits conchoidal fracture), Specific Gravity: 2.60 to 2.65
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Physical properties
Hardness: 7 on Mohs scale, Color: Varies widely including brown, grey, white, and black, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/cryptocrystalline quartz, Cleavage: None (exhibits conchoidal fracture), Specific Gravity: 2.60 to 2.65
Formation & geological history
Formed by the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of marine organisms (like radiolarians and diatoms) within sedimentary environments, primarily during the Cretaceous and other geological periods.
Uses & applications
Historically used by ancient humans for making stone tools and weapons (such as arrowheads and flint knapping); occasionally used as decorative aggregate or in landscaping.
Geological facts
Chert that is dark or black in color is commonly referred to as flint. It produces sparks when struck against steel due to its high hardness.
Field identification & locations
Can be identified in the field by its distinctive conchoidal fracture, sharp edges when broken, waxy luster, and high hardness that easily scratches glass.
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