sedimentary

Chert (variant Flint or Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: green-yellow, tan, and brown; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: green-yellow, tan, and brown
Luster: waxy to dull

Identified April 12, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: green-yellow, tan, and brown; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/chalk by silica-rich fluids. Common in sedimentary basins of various geological ages.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp edges; used in construction as aggregate and sometimes in jewelry (Jasper/Agate variants) or as a fire-starter (Flint).

Geological facts

Chert is so hard it can scratch steel. Because it breaks with a conchoidal (shell-like) fracture, it was the primary material used by prehistoric humans to create 'knapped' tools like scrapers and projectile points.

Field identification & locations

Identify by its waxy texture, extreme hardness (wont be scratched by a knife), and smooth, curved fracture surfaces. Found frequently in riverbeds or as nodules within limestone outcrops.