sedimentary

Chert (specifically Yellow/Brown Chert or Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Yellowish-brown, tan, or grey; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (hexagonal system at microscopic level); Cleavage: None (has characteristic conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Hardness: 7 on Mohs scale
Color: Yellowish-brown, tan, or grey
Luster: Dull to waxy

Identified March 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation in sedimentary environments. Common in marine limestone and chalk deposits from various geological ages, notably the Cretaceous and Paleozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modern uses include road surfacing, decorative garden stones, and as a raw material in ceramics. It is also a popular beginner rock for lapidary tumbling.

Geological facts

Chert has a unique property where it produces sparks when struck against steel, which made it vital for prehistoric survival and early firearms (flintlocks). The color is often derived from trace amounts of iron oxides like goethite or hematite.

Field identification & locations

Identified in the field by its hardness (it will scratch glass), smooth waxy feel, and 'shell-like' conchoidal fractures. Commonly found in riverbeds, gravel pits, and coastal cliffs. Collectors should look for unique banding or fossil inclusions.