sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 6.5-7 on Mohs scale; Color: typically grey, tan, or brown with a dull to waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: typically grey, tan, or brown with a dull to waxy luster

Identified April 9, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: typically grey, tan, or brown with a dull to waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the accumulation of microcrystalline silica, often from the remains of silica-secreting organisms like diatoms or radiolarians, or through chemical precipitation in marine or groundwater environments.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; and today used for road aggregate and decoratively in landscaping.

Geological facts

Chert has been used by humans for millions of years to create tools. Flint is a variety of chert. It can often contain micro-fossils only visible under a microscope.

Field identification & locations

Check for conchoidal (shell-like) fracturing and high hardness (it will scratch glass). Often found as nodules within limestone or as bedded layers in sedimentary sequences.