sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: tan, grey, reddish-brown; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none, exhibits conchoidal fracture; Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- tan, grey, reddish-brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, grey, reddish-brown; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none, exhibits conchoidal fracture; Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments, often replacing limestone or dolostone.
Uses & applications
Historically used for stone tools (arrowheads, scrapers); currently used as raw material for construction aggregate or for starting fires (flint variant).
Geological facts
Chert has been used by humans for over two million years to create sharp-edged tools due to its predictable conchoidal fracture patterns.
Field identification & locations
Identify in the field by its superior hardness (scratches glass), waxy appearance on fresh surfaces, and sharp, shell-like fracture edges. Common in sedimentary basins worldwide.
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