sedimentary

Chert (variant Flint/Novaculite)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: gray, tan, yellowish-brown; Luster: waxy to dull; Crystal Structure: Microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6 – 2.7

Hardness: 7 (Mohs scale)
Color: gray, tan, yellowish-brown
Luster: waxy to dull

Identified March 11, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: gray, tan, yellowish-brown; Luster: waxy to dull; Crystal Structure: Microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6 – 2.7

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of siliceous biological remains (like diatoms or radiolarians) in marine or lake environments. Often found as nodules or layers within limestone and chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Modern uses include abrasives, road construction material, and semi-precious lapidary work.

Geological facts

Chert was one of the most important raw materials for early humans. Its ability to produce sparks when struck against steel led to its use in 'flintlock' firearms. 'Novaculite' is a high-grade chert from Arkansas famous for making whetstones.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy feel, and characteristic shell-like (conchoidal) fracture edges. Commonly found in limestone outcrops or as smooth river pebbles. Collectors look for unique banding or 'picture' patterns.