sedimentary

Chert with Iron Staining

Microcrystalline quartz (SiO2) with iron oxide inclusions

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale. Color: Light grey/white with rusty orange and brown iron oxide staining. Luster: Vitreous to dull. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 - 2.65.

Hardness: 7 on the Mohs scale
Luster: Vitreous to dull

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of microscopic organisms (such as diatoms or radiolarians) in marine environments, followed by diagenesis. Iron staining occurs via groundwater percolation and weathering of iron-bearing minerals.

Uses & applications

Historically used for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Today collected as a lapidary specimen or rockhound find.

Geological facts

Chert has been utilized by humans for hundreds of thousands of years for toolmaking because it fractures in predictable, razor-sharp edges similar to obsidian and flint.

Field identification & locations

Can be identified by its extreme hardness (scratches glass easily), waxy to vitreous luster on fresh surfaces, and characteristic conchoidal fracture. Found worldwide in sedimentary sequences, particularly within limestone and chalk formations.