sedimentary

Chert / Flint

Chert (SiO2)

Hardness: 7 (Mohs); Color: Tan, white, buff with occasional translucent areas; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); SG: 2.65

Hardness: 7 (Mohs)
Color: Tan, white, buff with occasional translucent areas
Luster: Dull to waxy

Identified April 24, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Tan, white, buff with occasional translucent areas; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); SG: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in limestone or chalk beds. Most common in Paleozoic and Mesozoic sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used in construction aggregate and as a strike-stone for fire-starting. Occasionally used for decorative items.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, leading to its historical use as 'flint' in firearms and fire-lighting kits.

Field identification & locations

Identify in the field by its blocky or nodular shape, extremely sharp edges when broken, and characteristic curved (conchoidal) fracture pattern. It often occurs as nodules within softer limestone.