sedimentary

Chert (often called Flint or Jasper locally)

Chert (Microcrystalline Quartz, Formula: SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-yellow; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (features prominent conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, or grayish-yellow
Luster: Waxy to dull

Identified February 7, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-yellow; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (features prominent conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing carbonate materials in limestone or through the accumulation of siliceous organic remains (like diatoms or radiolarians). It can form as nodules or bedded layers across various geological periods from the Precambrian to the present.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and to start fires (flint and steel). Currently used in road construction, as an abrasive, and occasionally in lapidary work for jewelry or decor.

Geological facts

Chert is so hard it can scratch steel. It breaks with a conchoidal fracture, creating extremely sharp edges, which is why it was the primary material for tool-making in the Stone Age. Depending on color, it is frequently referred to as flint (black/dark grey) or jasper (red/brown).

Field identification & locations

Identify by its 'shell-like' curved fractures (conchoidal), waxy feel, and extreme hardness. Commonly found in limestone outcrops, riverbeds, and glacial till. Collectors look for unique colors or specimens that show signs of ancient human working (lithic debitage).