sedimentary
Chert
Silicon Dioxide (SiO2)
Hardness of 7 on the Mohs scale, typically gray, white, brown, or black in color, waxy to vitreous luster, microcrystalline or cryptocrystalline quartz structure, conchoidal fracture with no true cleavage, and specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically gray, white, brown, or black in color, waxy to vitreous luster, microcrystalline or cryptocrystalline quartz structure, conchoidal fracture with no true cleavage, and specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical accumulation of silica-rich skeletal remains of microscopic organisms like radiolarians and diatoms, or through the replacement of limestone by silica-bearing groundwater over millions of years.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-striking implements. Today used in crushed form for road construction and concrete aggregate.
Geological facts
Chert that occurs in nodules within chalk or limestone formations is frequently referred to as flint. Due to its conchoidal fracture, it can be chipped to produce extremely sharp edges.
Field identification & locations
Can be identified in the field by its hardness (scratches glass easily), smooth waxy appearance, and characteristic conchoidal fracture. Commonly found in limestone and chalk deposits worldwide.
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