sedimentary
Flint (or Chert with cortex)
Silicon dioxide (SiO2)
Hardness of 7 on the Mohs scale, typically gray, white, or black with a waxy or vitreous luster, conchoidal fracture, and no cleavage. Features a chalky white outer cortex layer.
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Physical properties
Hardness of 7 on the Mohs scale, typically gray, white, or black with a waxy or vitreous luster, conchoidal fracture, and no cleavage. Features a chalky white outer cortex layer.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions in marine environments during the Cretaceous period and other epochs.
Uses & applications
Historically used for making stone tools, arrowheads, and spark-producing fire starters (flint and steel). Today used in landscaping, abrasives, and as a collector's specimen.
Geological facts
Flint is a hard, tough variety of microcrystalline quartz. Its ability to fracture with extremely sharp edges made it one of the most important materials for early human technology during the Stone Age.
Field identification & locations
Easily identified in the field by its distinctive chalky white exterior (cortex), conchoidal fracture showing a dark, glassy interior, and high hardness that scratches glass. Commonly found embedded in chalk cliffs and chalk stream beds.
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