sedimentary

Chert or flint (weathered brown variety)

Microcrystalline quartz, SiO₂ (chalcedonic quartz)

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, earthy brown/tan color, dull to waxy luster, and no visible crystals or cleavage. It commonly breaks with a curved conchoidal fracture, though this specimen appears heavily weathered and porous.

Identified August 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica replaces carbonate sediment or accumulates as biogenic silica in sedimentary beds, commonly during the Paleozoic–Cenozoic eras. Brown coloration may result from iron oxides and surface weathering.

Uses & applications

Used historically for sharp tools and arrowheads; today it is mainly a teaching, lapidary, landscaping, and collecting material. Attractive varieties can be polished for ornamental objects.

Geological facts

Chert can preserve fossils and may occur as nodules or continuous beds in limestone. Flint is generally a dark, dense chert, while lighter or brown forms are often simply called chert.

Field identification & locations

Check for hardness sufficient to scratch glass, a waxy surface, and sharp conchoidal edges; it should not fizz strongly in dilute hydrochloric acid. Common worldwide, especially in limestone regions; exact identification is limited without testing.