sedimentary
Chert with Iron Staining
Microcrystalline quartz (SiO2) with iron oxide inclusions
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
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Physical properties
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.
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.
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