sedimentary
Flint (or Chert)
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, color ranges from brown, tan, and grey to black, vitreous to waxy luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, color ranges from brown, tan, and grey to black, vitreous to waxy luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions derived from sponge spicules or microorganisms during the Cretaceous and other sedimentary periods.
Uses & applications
Historically used for making stone tools, arrowheads, and spark-producing fire starters (flint and steel); currently used in abrasive grit, road construction, and decorative landscaping.
Geological facts
Flint is extremely durable and breaks with a very sharp conchoidal edge, making it the material of choice for prehistoric stone implements across many cultures.
Field identification & locations
Can be identified by its distinctive conchoidal fracture, waxy luster, and high hardness which easily scratches glass. Commonly found as nodules within chalk or limestone formations and as pebbles on beaches.
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