sedimentary

Chert (Flint)

Chert (Cryptocrystalline Quartz, SiO2)

Hardness: 7 (Mohs scale). Color: Ranges from gray, black, brown to tan. Luster: Waxy to dull. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Ranges from gray, black, brown to tan
Luster: Waxy to dull

Identified March 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids within limestone or chalk beds. Most specimens date from the Paleozoic to Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a component in certain ceramics and glass manufacturing.

Geological facts

Flint is a variety of chert that was essential to human survival for millennia, used both for weaponry and for striking against steel to create sparks for fire. The term 'flint' is often reserved for chert found in chalk or marly limestone.

Field identification & locations

Identify in the field by its distinct shell-like (conchoidal) fracture pattern and its ability to scratch glass. It often occurs as rounded nodules or layered beds in limestone outcrops. Frequently found in riverbeds or coastal areas.

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