sedimentary

Chert or flint fragment

Microcrystalline quartz (SiO₂), commonly chalcedony with cryptocrystalline quartz

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, waxy to dull luster, gray-brown color, very fine-grained texture, no visible cleavage, and conchoidal fracture with sharp edges. The specimen appears weathered and possibly lightly patinated.

Identified August 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by silica replacement or precipitation in sedimentary rocks, especially limestone and chalk, from silica-rich groundwater or biogenic remains. Deposits range from Precambrian to recent geological ages.

Uses & applications

Used historically for tools, arrowheads, and fire-starting; modern uses include aggregate, abrasives, decorative stone, and lapidary work. Attractive patterned varieties may be collected or polished.

Geological facts

Chert is the broader term; “flint” commonly refers to dark, high-quality chert associated with chalk. Freshly fractured surfaces are often glassy and sharply conchoidal.

Field identification & locations

Identify it by testing for glass-scratching hardness, lack of visible grains, and conchoidal fracture; it should not fizz with dilute hydrochloric acid. Common worldwide in limestone, chalk, and sedimentary formations.