sedimentary
Chert / Flint
Chert (Cryptocrystalline Silica, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, or dark blue-gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, or dark blue-gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, or dark blue-gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires (flint). Currently used in road surfacing, as grinding media in ball mills, and for decorative lapidary work.
Geological facts
Flint is a variety of chert that was essential to prehistoric humans for making arrowheads and knives because of its razor-sharp conchoidal fracture edges.
Field identification & locations
Identify by its 'shell-like' (conchoidal) curved fractures and its ability to scratch glass easily. It is commonly found in riverbeds or eroding out of sedimentary rock layers.
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