sedimentary

Chert (variations include Flint/Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness (7 on Mohs scale), Color: tan, grey, brown, white; Luster: waxy to dull; Crystal structure: hexagonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Color: tan, grey, brown, white
Luster: waxy to dull

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness (7 on Mohs scale), Color: tan, grey, brown, white; Luster: waxy to dull; Crystal structure: hexagonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation from silica-rich fluids in sedimentary basins. Often found as nodules or layers within limestone or chalk.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracture. Today used as road aggregate, in landscaping, and some high-quality varieties are used in lapidary work.

Geological facts

Chert has been used by humans for over 2 million years. It is chemically identical to quartz but has an entirely different structural texture. Flint is a specific variety of chert typically found in chalk deposits.

Field identification & locations

Identify in the field by its hardness (scratches steel/glass), smooth conchoidal fracture edges (sharp like glass), and waxy appearance. Commonly found in stream beds and outcropping from limestone cliffs.