sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, white, and brown with orange iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, white, and brown with orange iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, white, and brown with orange iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments during various geological periods, often occurring as nodules or bedded deposits.
Uses & applications
Historically used for stone tools due to its sharp edges; currently used for road surfacing, as an abrasive, and occasionally in lapidary work as a gemstone or for decorative gravel.
Geological facts
Chert is a tough, durable rock that often preserves microfossils. It has been used by humans for hundreds of thousands of years to create arrowheads, spear points, and scrapers because of its predictable fracturing pattern.
Field identification & locations
Identify by its hardness (it will scratch glass), its conchoidal (shell-like) fracture, and its smooth, fine-grained texture. It is often found in limestone or chalk beds and along riverbanks or in gravel pits.
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