sedimentary

Chert or flint

Microcrystalline quartz (SiO₂), likely chalcedony-rich chert

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque gray-brown with a tan weathered cortex, dull to waxy luster, and no visible cleavage. It is dense, fine-grained, and commonly breaks with smooth conchoidal fractures and sharp edges.

Identified August 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when silica-rich marine or groundwater deposits replaced limestone, chalk, or accumulated as siliceous ooze; individual pieces may range from Paleozoic to Cenozoic in age. The tan outer rind likely reflects weathering or a natural cortex.

Uses & applications

Used historically for sharp tools, arrowheads, and fire-starting; today it is mainly a collector, lapidary, or teaching specimen. It has limited construction value compared with bulk aggregate.

Geological facts

The image shows a weathered, naturally fractured fragment rather than a diagnostic crystal specimen. Flint is technically a dark variety of chert, often associated with chalk deposits.

Field identification & locations

Identify it by its very fine texture, waxy appearance, hardness sufficient to scratch glass, and conchoidal fracture; it commonly occurs in limestone, chalk, gravel beds, and glacial till. Exact identification would benefit from a fresh broken surface and locality information.