sedimentary

Chert (specifically Flint)

Chert (Microcrystalline or Cryptocrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Brown, tan, grey, and white banding; Luster: Waxy to vitreous (glassy) on fresh breaks; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65

Hardness: 7 on Mohs scale
Color: Brown, tan, grey, and white banding
Luster: Waxy to vitreous (glassy) on fresh breaks

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary basins. Often found as nodules within limestone or chalk beds. Geological age varies from Precambrian to Recent.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to sharp conchoidal edges and as fire-starters. Modernly used as a decorative stone, in lapidary work for jewelry (cabochons), and as a component in road fill or concrete aggregate.

Geological facts

Flint was one of the most important minerals for early human survival, used for both weaponry and starting fires. When struck against steel, it creates sparks. The sharp edges of a fresh break can be thinner than a surgical steel scalpel.

Field identification & locations

Identify by its 'shell-like' (conchoidal) fracture pattern and its ability to scratch glass. Look for it in areas with limestone outcroppings or as smoothed nodules in riverbeds. These specific specimens show a classic 'rind' or weathered cortex on the outside.