sedimentary

Flint or chert, likely iron-stained

Microcrystalline quartz (SiO₂), commonly called flint when dark and nodular

AI-generated identification · may be incorrect

Hardness about 7 Mohs; reddish-brown to black, waxy-to-glassy luster, opaque to translucent edges, and conchoidal fracture. It lacks visible cleavage and consists mainly of cryptocrystalline quartz, with iron-oxide staining and possibly brecciated/weathered crust.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by silica replacement or precipitation in sedimentary rocks, especially limestone and chalk, commonly during the Mesozoic or younger. The rusty color reflects oxidation of iron-bearing impurities; the pictured piece appears naturally fractured or roughly knapped, not a polished gemstone.

Uses & applications

Historically used for sharp tools, fire-starting, and arrowheads; today it is mainly a decorative, lapidary, or teaching specimen. It is not typically used as an architectural stone.

Geological facts

Fresh fractures are extremely sharp and show curved, shell-like surfaces; reddish varieties may be sold as jasper, although jasper is generally more opaque and iron-rich. A steel file should not scratch it, while quartz or glass can scratch it.

Field identification & locations

Common in chalk, limestone, and gravel deposits worldwide, including England, France, the U.S. Midwest, and Texas. Check for conchoidal fracture, waxy texture, and a white streak; confirm with hardness and, if necessary, thin-section or X-ray analysis.