sedimentary

Chert (Flint)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or smoky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, or smoky grey
Luster: Waxy to vitreous

Identified April 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, or smoky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or diatoms) in marine environments. It occurs often as nodules or bedded layers in limestone or chalk.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; industrially used as an abrasive, and in some jewelry as cabochons.

Geological facts

Chert has a distinctive conchoidal fracture, which means it breaks like glass, producing very sharp edges. This property made it the primary material for prehistoric survival tools globally.

Field identification & locations

Identify in the field by its smooth, waxy surface and the way it chips into sharp, curved flakes. It is frequently found in limestone outcrops or as rounded 'river rocks' in creek beds.