sedimentary

Chert (Nodular Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or earthy yellowish-brown; Luster: Dull to waxy; Structure: Microcrystalline with no visible grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, or earthy yellowish-brown
Luster: Dull to waxy

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of carbonate rocks (like limestone or dolomite) by silica-rich fluids or through the accumulation of siliceous remains such as diatoms or radiolarians. Often found in Paleozoic to Cenozoic strata.

Uses & applications

Primarily used in construction as road base or aggregate. Historically used for making tools like arrowheads and scrapers due to its sharp edges when broken. Also used in decor or landscaping.

Geological facts

Chert is chemically identical to quartz and flint. Flint is generally the dark variety, while chert is the lighter, earth-toned variety. It is one of the most durable rocks, often surviving long after the surrounding limestone has eroded away.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and steel) and its smooth, shell-like (conchoidal) breakage patterns. Common in creek beds and limestone outcrops. Collectors look for pieces with unique banding or fossils trapped inside.