sedimentary

Chert (often called Flint or Jasper)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or earthy yellow; Luster: Dull to waxy; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7

Hardness: 7 on Mohs scale
Color: Tan, brown, or earthy yellow
Luster: Dull to waxy

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/dolomite. This specimen appears to be a nodular variety common in sedimentary basins throughout geological history.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in jewelry (as jasper), as a flux in glass making, and as a durable road aggregate or gemstone polishing material.

Geological facts

Because of its conchoidal fracture, it breaks into pieces with very sharp edges, leading ancient civilizations to use it for arrowheads and knives. Flint is a specific variety of chert often found in chalk or marly limestone.

Field identification & locations

Identify in the field by its hardness (it can scratch glass), its smooth 'conchoidal' (shell-like) fracture surfaces, and its waxy feel. It is commonly found in riverbeds, agricultural fields, or weathered out of limestone cliffs.