sedimentary

Chert (specifically Flint or Common Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, green, brown, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, green, brown, or white
Luster: Waxy to dull

Identified April 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, green, brown, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in sedimentary environments such as limestone or chalk beds. Most specimens found today date from the Paleozoic to Mesozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used in construction aggregate and as a spark-generator in flintlock firearms.

Geological facts

Chert is so hard it can scratch steel. When struck against steel or iron pyrites, it produces sparks, which led to its vital historical role in starting fires and firing primitive guns.

Field identification & locations

Identify in the field by its smooth, waxy surface and characteristic shell-like (conchoidal) curved fractures. It is commonly found as nodules in limestone outcrops or as river-worn pebbles.