sedimentary

Chert (Flint/Jasper variety)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey, brown, and reddish-orange due to iron oxides; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 Mohs scale
Color: Grey, brown, and reddish-orange due to iron oxides
Luster: Waxy to dull

Identified June 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from fluids within sedimentary beds, such as limestone or chalk, often during the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Currently used in road construction, as jewelry (when patterned), and as flint for survival fire-starting.

Geological facts

Unlike many rocks, chert breaks with a conchoidal fracture, similar to glass, which allows it to produce edges thinner than a surgeon's steel scalpel. The reddish coloration in this specimen is likely due to hematite or goethite impurities.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture surfaces. Frequently found in riverbeds, glacial tills, and as nodules within carbonate rock outcrops.

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