sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brownish-red to tan; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Brownish-red to tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Brownish-red to tan; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in marine environments, often replacing original limestone or chalk.
Uses & applications
Used historically for stone tools and weapons (flintknapping); currently used in jewelry as cabochons, as landscaping stone, and in construction aggregates.
Geological facts
Chert is one of the most durable rocks and was essential to early human survival for making spear tips and arrowheads. It can spark when struck against steel.
Field identification & locations
Identify in the field by its distinct conchoidal (shell-like) fracture, extreme hardness (scratches glass), and waxy texture. Commonly found in riverbeds or as nodules in limestone outcrops.
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