sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: White, cream, and tan. Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Hardness: 7 on Mohs scale
Color: White, cream, and tan
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: White, cream, and tan. Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Formation & geological history

Formed primarily in marine environments where silica-rich fluids (often from radiolarians or sponges) precipitate within limestone or chalk beds. It typically develops as nodules or bedded layers in early to mid-geologic periods.

Uses & applications

Historically used for stone tools and fire-starting. Currently used in road construction as aggregate, as a gemstone (jasper/agate varieties), and in chemical manufacturing for grinding media.

Geological facts

Chert is so hard it can scratch glass and steel. When struck with steel, it produces sparks, which led to its prominent historical use in flintlock firearms.

Field identification & locations

Identify by its conchoidal (shell-like) fracture patterns and sharp edges. It is commonly found in sedimentary basins and riverbeds where limestone has eroded away. For collectors, look for its smooth, waxy feel compared to surrounding limestone.