sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: tan, grey, and black banding. Luster: waxy to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 7 (Mohs scale), Color: tan, grey, and black banding
Color: tan, grey, and black banding
Luster: waxy to dull

Identified June 18, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, grey, and black banding. Luster: waxy to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation. The bands represent changes in sediment composition over time, often during the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include decorative landscaping, flint-knapping enthusiasts, and occasionally as a low-cost gemstone for cabochons.

Geological facts

Chert is so durable that it often survives intense weathering that destroys other rocks. The spark-producing property when struck against steel made it essential for early firearms (flintlocks).

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and ability to scratch glass. Commonly found in limestone or dolomite beds as nodules or layers. Look for smooth, waxy surfaces on broken edges.