sedimentary
Chert (or Flint)
Microcrystalline Quartz (SiO2)
Hardness of 7 on the Mohs scale. Colors typically range from grey, white, brown, to light tan or yellowish hues, often showing waxy to vitreous luster. It features conchoidal fracture and lacks cleavage.
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Physical properties
Hardness of 7 on the Mohs scale. Colors typically range from grey, white, brown, to light tan or yellowish hues, often showing waxy to vitreous luster. It features conchoidal fracture and lacks cleavage.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of marine organisms such as diatoms and radiolarians over millions of years.
Uses & applications
Historically used for making stone tools, arrowheads, and spark generation in firearms. Currently used in road construction, concrete aggregate, and occasionally in decorative landscaping.
Geological facts
Chert and flint are chemically identical forms of microcrystalline quartz, with 'flint' typically referring to darker varieties found in chalk deposits. Because of its predictable conchoidal fracture, it was one of the most prized materials for prehistoric tool-making.
Field identification & locations
Easily identifiable in the field by its extreme hardness, smooth waxy surface texture, and sharp conchoidal fracture edges. Commonly found embedded in sedimentary formations like limestone and chalk cliffs or as weathered pebbles in riverbeds.
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