sedimentary
Chert (Field Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark grey to blackish; Luster: Waxy to dull; Breakdown: Conchoidal fracture (shell-like curves); Crystal structure: Cryptocrystalline; Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Dark grey to blackish
- Luster
- Waxy to dull
Identified More sedimentary →
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark grey to blackish; Luster: Waxy to dull; Breakdown: Conchoidal fracture (shell-like curves); Crystal structure: Cryptocrystalline; Specific Gravity: 2.65.
Formation & geological history
Formed as nodules or layered deposits in sedimentary rocks (typically limestones) through the accumulation of silica-rich organic remains or chemical precipitation. Most are hundreds of millions of years old.
Uses & applications
Used historically for stone tools (arrowheads, scrapers) due to its sharp edges; used today in road construction, as flint for fire-starting, and occasionally in jewelry as gemstones (Jasper is a variety of chert).
Geological facts
Because it breaks with a conchoidal fracture, it creates edges sharper than a steel scalpel. Ancient civilizations relied on chert for survival tools for over two million years.
Field identification & locations
Identify by its waxy surface and the way it chips into sharp, curved flakes. Found globally in limestone outcrops, stream beds, and gravel pits. Collectors look for unique colors or evidence of ancient tool-making (knapping).
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