sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically tan, brown, or white; Luster: waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: none (conchoidal fracture).

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

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically tan, brown, or white; Luster: waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: none (conchoidal fracture).

Formation & geological history

Forms as a chemical precipitate or through the replacement of other materials in marine or lacustrine environments. It is often found as nodules or layers within limestone and chalk.

Uses & applications

Historically used for making stone tools (arrowheads). Today used as a road aggregate, in landscaping, and some colorful varieties (like Jasper) are used in jewelry.

Geological facts

Chert is so hard that it can strike sparks against steel. Because of its conchoidal fracture, it produces very sharp edges, leading to its extensive use by prehistoric humans for hunting tools.