sedimentary

Chert (Iron-stained variant)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, cream, with reddish-orange iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, cream, with reddish-orange iron staining
Luster: Waxy to dull

Identified March 15, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, cream, with reddish-orange iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. Can range from Precambrian to Cenozoic in age.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modernly used as road aggregate, in landscaping, and as a low-cost lapidary material for tumbling.

Geological facts

Because of its hardness and conchoidal fracture, it was the primary material used by prehistoric humans to create arrowheads, scrapers, and knives. It is also known as 'flint' when found in chalk or marl.

Field identification & locations

Identify in the field by its hardness (it scratches glass easily) and its shell-like (conchoidal) breakage patterns. Often found as nodules in limestone or as distinct bedded layers in riverbeds.