sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: light grey to tan; Luster: waxy or dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: none; Fracture: conchoidal (shell-like)

Hardness: 7 on Mohs scale
Color: light grey to tan
Luster: waxy or dull

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: light grey to tan; Luster: waxy or dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: none; Fracture: conchoidal (shell-like)

Formation & geological history

Formed in marine environments through the precipitation of silica from seawater or the accumulation of silica-rich skeletal remains (like radiolarians or diatoms). Found in sedimentary rock layers such as limestone.

Uses & applications

Historically used for making stone tools like arrowheads and scrapers. Currently used in construction aggregate, road base, and as decorative gravel. High-quality specimens are used for lapidary work.

Geological facts

Chert is essentially the same mineral as flint, though 'flint' usually refers to dark nodules found in chalk. It provides the sharpest natural edge known to man because of its fine grain structure.

Field identification & locations

Identify by its smooth, waxy surface and conchoidal fracture patterns that leave sharp, curved edges. It will easily scratch glass and cannot be scratched by a steel knife. Common globally in sedimentary basins.