sedimentary
Chert (with Iron Staining)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Grey with reddish-orange iron oxide staining, Luster: Dull to waxy, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Grey with reddish-orange iron oxide staining, Luster: Dull to waxy, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation within marine or freshwater sediments. It is often found in limestones and can date from the Precambrian to the present.
Uses & applications
Historically used for making stone tools (arrowheads). Modernly used as road aggregate, in landscaping, and as a low-cost lapidary material.
Geological facts
Chert is extremely durable and chemically stable. The red/orange band is likely Limonite or Hematite staining from the oxidation of iron-bearing minerals during weathering.
Field identification & locations
Identify in the field by its superior hardness (scratches glass), smooth conchoidal fracture, and lack of reaction to acid. It is found globally in sedimentary basins.
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