sedimentary

Chert (Yellow Chert/Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan to yellow; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan to yellow
Luster: Waxy to dull

Identified May 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan to yellow; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwater within limestone or chalk beds. Most specimens occur in Paleozoic to Mesozoic sedimentary layers.

Uses & applications

Historically used for stone tools and reaching fire (flint). Currently used in jewelry as tumbled stones, gravel in construction, and as decorative landscaping stones.

Geological facts

Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges for knives and arrowheads. Yellow varieties are often colored by iron oxide (limonite) impurities.

Field identification & locations

Identify in the field by its waxy texture, smooth conchoidal fractures, and extreme hardness (it will scratch glass). Commonly found in stream beds or as nodules protruding from weathered limestone cliffs.