sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: typically tan, brown, or gray; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65

Hardness: 7 Mohs scale
Color: typically tan, brown, or gray
Luster: waxy to dull

Identified June 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily by the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or by chemical precipitation from silica-rich groundwater within limestone or chalk beds.

Uses & applications

Historically used for making stone tools and arrowheads because of its sharp conchoidal fracture. Modern uses include road surfacing and as a component in glass manufacturing.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use as flint in firearms and fire-starting kits.

Field identification & locations

Identify in the field by its smooth, shell-like fracture surfaces and its ability to scratch glass. It is often found as nodules within limestone or as bedded deposits in riverbeds.