sedimentary

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, or white (in this specimen); Luster: Waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, beige, or white (in this specimen)
Luster: Waxy to dull

Identified March 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of marine organisms (like diatoms or radiolarians). It occurs primarily within limestone or chalk beds and can date from the Precambrian to the Cenozoic era.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used in road construction, as an abrasive, and sometimes as a minor gemstone or decorative rock.

Geological facts

Because it breaks with a conchoidal (shell-like) fracture, it produces edges that can be sharper than a surgical scalpel. It was one of the first materials traded by humans in prehistoric times.

Field identification & locations

Identify in the field by its hardness (it will scratch glass/steel), waxy texture, and sharp, curved edges when broken. It is extremely common in areas with limestone bedrock, such as the Midwestern United States or the chalk cliffs of Europe.

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