sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-orange due to iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Brown, tan, and reddish-orange due to iron staining
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-orange due to iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed in sedimentary environments, specifically through the chemical replacement of carbonate rocks or the accumulation of silica-rich organic remains. In the coastal UK (matching the 51.8N, 1.1E location), these are often found as nodules in Cretaceous Chalk deposits.

Uses & applications

Historically used for stone tools (knapping) and as gunflints; currently used as construction aggregate, road ballast, and occasionally for decorative landscaping.

Geological facts

Flint and Chert are essentially the same material, with the term 'Flint' often reserved for nodules found in Chalk. Because it breaks with a conchoidal fracture, it creates edges sharper than a steel scalpel.

Field identification & locations

Identify by its smooth, waxy interior texture contrasted by a rough, often white or orange outer weathering rind (cortex). It is extremely common along the East Anglian and Essex coasts of England.