sedimentary

Chert Nodule in Limestone

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: tan, brownish, or yellowish; Luster: waxy to dull; Structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves)

Hardness: 7 (Mohs scale), Color: tan, brownish, or yellowish
Color: tan, brownish, or yellowish
Luster: waxy to dull

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, brownish, or yellowish; Luster: waxy to dull; Structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves)

Formation & geological history

Formed through the accumulation of silica-rich fluids within carbonate sediment or by the replacement of calcium carbonate by silica during diagenesis in marine environments.

Uses & applications

Used historically for stone tools and fire-starting (flint); currently used in road construction, as an abrasive, and sometimes for decorative landscaping.

Geological facts

Chert is so hard it can scratch steel and was used by prehistoric humans to make arrowheads and scrapers because of its sharp conchoidal fracture edges.

Field identification & locations

Look for a hard, waxy-looking lump embedded in softer, grayish limestone or chalk; it will be noticeably more resistant to weathering than the surrounding rock.