sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: typically brown, gray, or black; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture; Specific gravity: 2.5-2.8.

Hardness: 6
Color: typically brown, gray, or black
Luster: waxy to dull

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation from silica-saturated waters. It occurs as nodules or beds within limestone or chalk formations.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modern uses include road surfacing, glass manufacturing, and as a component in certain ceramics. Smaller, colorful specimens are used in jewelry or as decorative stones.

Geological facts

Chert was one of the most important geological materials for early humans; its ability to fracture into razor-sharp edges revolutionised tool-making. It is so hard that it can strike sparks from steel, leading to its name 'flint' in specific contexts.

Field identification & locations

Identify in the field by its smooth, waxy feel and distinctive curved (conchoidal) breaks. It is commonly found in riverbeds, glacial till, and coastal cliffs. It is widely distributed globally, notably in the Chalk formations of Europe and the limestone regions of the USA.