sedimentary

Chert (specifically Flint or Common Chert)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Varying shades of gray, brown, and tan; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline/cryptocrystalline); Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Varying shades of gray, brown, and tan
Luster: Waxy to dull

Identified April 8, 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 the chemical precipitation of silica in marine or groundwater environments. Can be found in nodules or bedded layers within limestone or chalk deposits.

Uses & applications

Historically used for stone tools (arrowheads, knives) and strike-a-lights for fire starting. Modern uses include road aggregate, concrete filler, and occasional use in jewelry/gemstone tumbling if the color is attractive.

Geological facts

Chert and flint were among the first materials used by early humans to manufacture tools due to the razor-sharp edges created by conchoidal fracturing. 'Flint' is a term typically reserved for chert found in chalk formations.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass and steel), and curved, shell-like (conchoidal) fracture patterns. It is extremely common in sedimentary basins worldwide.

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Brecciated Chert (Microcrystalline Silica)

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