sedimentary
Chert (Flint)
Chert (Microcrystalline or cryptocrystalline Silica, SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
- Hardness
- 6
- Color
- Brown, tan, gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
Formation & geological history
Formed primarily from the precipitation of silica in sedimentary environments, often from the remains of siliceous organisms like diatoms or radiolaria, or through chemical replacement in limestone.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges. Modernly used in road construction, as jewelry (jasper), and as a component in flintlock firearms.
Geological facts
Chert is so hard it can strike sparks from steel. It has been used by humans for hundreds of thousands of years to create arrowheads and scrapers.
Field identification & locations
Identified in the field by its smooth, waxy surface and its tendency to break into sharp, curved (conchoidal) flakes. Common in river beds and limestone outcrops.
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