sedimentary
Chert (Quartz Variety)
Microcrystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Cream, tan, or light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Cream, tan, or light brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Cream, tan, or light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in sedimentary basins. Primarily found in marine limestone or dolostone.
Uses & applications
Historically used for stone tools (knapping); modernly used for road aggregate and as an abrasive in some industrial processes.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans because of its ability to fracture into extremely sharp edges for blades and arrowheads.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture, extreme hardness, and smooth, waxy surface. Often found in nodes or beds within limestone formations.
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