sedimentary

Weathered flint or chert fragment

Microcrystalline quartz (SiO₂), likely chert/flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dull to waxy luster, gray-tan exterior with rusty iron-oxide staining and a cream-to-brown interior. Microcrystalline quartz has no visible cleavage and commonly breaks with conchoidal fractures; the surface appears naturally weathered and possibly waterworn.

Identified August 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica precipitates or replaces material in sedimentary rocks, often during the Paleozoic–Cenozoic eras; flint is a dark variety commonly associated with chalk. The rounded shape and abrasion suggest transport by water or glacial action.

Uses & applications

Historically used for sharp tools, fire-starting, and knapping; today it is mainly a teaching or collecting specimen, though chert is also used locally as aggregate and road material.

Geological facts

Freshly broken chert can produce very sharp edges and may show a translucent margin. The reddish coloration is likely limonite or hematite staining rather than the primary mineral.

Field identification & locations

Identify it by its very hard, nonporous character, waxy texture, and sharp conchoidal fracture; it should scratch glass and resist a steel knife. Common in limestone, chalk, gravel beds, river deposits, and glacial till.