sedimentary
Chert
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 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
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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.
Field identification & locations
Identify by its hardness (scratches glass), waxy appearance, and conchoidal (curved) fracture surface. Common in sedimentary basins worldwide.
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