sedimentary

Chert (Banded Variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Cream, tan, gray, and brown with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.65.

Hardness: 7 on Mohs scale
Color: Cream, tan, gray, and brown with distinct banding
Luster: Waxy to dull

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (such as diatoms or radiolarians) or the chemical precipitation of silica from groundwater within limestone or chalk beds. This specimen displays secondary banding common in nodules formed during diagenesis.

Uses & applications

Historically used for making stone tools (flintknapping); currently used as building stone, road surfacing, and as a semi-precious gemstone when polished (Jasper).

Geological facts

Chert is so hard it can easily scratch glass and was a primary material for prehistoric cultures to create sharp-edged blades and arrowheads because of its predictable conchoidal fracturing.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife), smooth waxy feel, and curved 'shell-like' fracture patterns. Common in sedimentary basins worldwide, particularly in the Midwestern and Western United States.

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