sedimentary
Chert (Commonly known as Flint/Jasper)
Microcrystalline Quartz (SiO2) with iron oxide inclusions
Hardness: 6.5-7 (Mohs). Color: Opaque reddish-brown and mustard yellow. Luster: Waxy to dull. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque reddish-brown and mustard yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Opaque reddish-brown and mustard yellow. Luster: Waxy to dull. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed primarily through the chemical precipitation of silica in marine environments or by the replacement of calcium carbonate in sedimentary layers. This region near the coast of Essex and Suffolk is rich in Cretaceous and Paleogene sediments containing significant flint and chert deposits.
Uses & applications
Historically used for stone tools due to its sharp edges; currently used for decorative stone, tumbling, aquarium gravel, and road construction.
Geological facts
The reddish-brown color is caused by the presence of iron oxide (hematite or limonite) staining the silica. Flint which is a type of chert has been the most important rock for human technology for over 2 million years.
Field identification & locations
Identify by its smooth, waxy texture and conchoidal (shell-like) fracture patterns. It is very common on the beaches and in the fields of Eastern England. It cannot be scratched by a steel knife.
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