sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray in this specimen; Luster: waxy to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically tan, brown, or gray in this specimen
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray in this specimen; Luster: waxy to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture.
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like radiolarians or diatoms) or through chemical precipitation in marine environments where silica replaces carbonate material.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; used today as a decorative aggregate in landscaping and as a component in road construction.
Geological facts
Chert is so hard it can scratch steel and was used by prehistoric humans globally to create fire when struck against iron pyrites or steel, due to its ability to produce sparks.
Field identification & locations
Check for conchoidal (shell-like) fractures and high hardness. It will scratch glass easily. Commonly found in limestone or chalk beds as nodules.
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