sedimentary

Chert (Quartz Variety)

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown, or light grey with pinkish banding; Luster: Dull to waxy; Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Tan, beige, brown, or light grey with pinkish banding
Luster: Dull to waxy

Identified March 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or by chemical precipitation from groundwater within limestone or chalk beds. Often occurring as nodules or beds in sedimentary layers from various geological ages, notably the Paleozoic and Mesozoic eras.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; modernly used as construction aggregate, road base, and occasionally as decorative landscaping stone or for primitive fire-starting (flint).

Geological facts

Chert is so durable that it often remains in riverbeds long after the surrounding limestone has eroded away. The dark variety of chert is most commonly known as 'flint.' It was the primary technological material for humanity for over two million years.

Field identification & locations

Identify in the field by its smooth, waxy texture and distinctive 'shell-like' curved (conchoidal) fractures. It will easily scratch glass but cannot be scratched by a steel knife. Commonly found in riverbeds, gravel pits, and eroding limestone outcrops.