sedimentary
Chert (often called Flint or Jasper if reddish)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: White, gray, and reddish-brown, Luster: Vitreous to waxy, Structure: Cryptocrystalline, Fracture: Conchoidal, Cleavage: None
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Physical properties
Hardness: 7 (Mohs), Color: White, gray, and reddish-brown, Luster: Vitreous to waxy, Structure: Cryptocrystalline, Fracture: Conchoidal, Cleavage: None
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms or via chemical precipitation in sedimentary basins over millions of years.
Uses & applications
Used historically for stone tools and weapons (arrowheads); currently used in road surfacing, abrasives, and as decorative gravel. Semi-precious versions like Jasper are used in jewelry.
Geological facts
Chert breaks with a conchoidal fracture, creating very sharp edges, which made it the primary material for early human tools and weapons. It is also a key component in finding fossils in certain formations.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), its smooth, shell-like fracture pattern, and often a waxy appearance. Commonly found in limestone or chalk beds.
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