sedimentary
Chert / Flint
Cryptocrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale. Colors range from tan, brown, white, and grey to dark blue-black. Displays a waxy to vitreous luster and a distinct conchoidal fracture. Microscopic quartz crystal structure with no visible cleavage.
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Physical properties
Hardness of 7 on the Mohs scale. Colors range from tan, brown, white, and grey to dark blue-black. Displays a waxy to vitreous luster and a distinct conchoidal fracture. Microscopic quartz crystal structure with no visible cleavage.
Formation & geological history
Formed through the chemical replacement of limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of marine organisms like diatoms and radiolarians in deep marine environments.
Uses & applications
Historically used for stone tools, arrowheads, and striking fire due to its conchoidal fracture and sharp edges. Today used in abrasive products, road aggregate, and as decorative landscape or lapidary stones.
Geological facts
Known as flint when found as nodules in chalk and chert when found in bedded limestone. It was one of the earliest materials manipulated by early humans for weaponry and fire-making.
Field identification & locations
Easily identified in the field by its hardness (scratches glass), sharp conchoidal edges, and waxy luster. Commonly found embedded in limestone or chalk formations worldwide.
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