sedimentary

Chert / Flint

Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, tan, or brown with white speckles; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, tan, or brown with white speckles
Luster: Waxy to vitreous

Identified March 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, tan, or brown with white speckles; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like sponge spicules or radiolarians) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds spanning from the Precambrian to the Cenozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include construction aggregate, gemstones (when colorful), and high-strength industrial grinding media.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for the 'Stone Age' and was later vital for fire-starting and flintlock firearms due to its ability to create sparks when struck against steel.

Field identification & locations

Identify by its 'conchoidal' (shell-like) fracture pattern and its ability to scratch glass easily. Commonly found in riverbeds or eroded out of limestone cliffs. Collector tips: look for smooth, waxy surfaces and translucent edges.