sedimentary

Chert (often called Flint when dark)

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, white, or red (due to iron oxides); Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 on Mohs scale
Color: Tan, brown, white, or red (due to iron oxides)
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of microscopic organisms like diatoms or radiolaria, or via chemical precipitation from silica-rich fluids in limestone or chalk beds. Often Paleozoic to Mesozoic in age.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as road material, in construction aggregate, and as a component in ceramics.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which led to its historical use in flintlock firearms and fire-starting kits.

Field identification & locations

Identify by its waxy texture and conchoidal (shell-like) fracture patterns. Look for it in limestone outcrops or as rounded nodules in stream beds and coastal areas.