sedimentary
Chert (Iron-stained)
Microcrystalline silica (SiO2) with Hematite/Limonite
Mohs hardness of 7, color ranges from white/cream to rusty orange-brown due to iron oxidation, waxy to dull luster, conchoidal fracture, very fine-grained texture.
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Physical properties
Mohs hardness of 7, color ranges from white/cream to rusty orange-brown due to iron oxidation, waxy to dull luster, conchoidal fracture, very fine-grained texture.
Formation & geological history
Formed in marine or freshwater environments via the accumulation of siliceous oozes or the replacement of limestone/dolomite by silica. The rusty color indicates later exposure to oxygen and iron-rich groundwater.
Uses & applications
Historically used for stone tools (arrowheads). Currently used as road aggregate, architectural stone, and occasionally for lapidary work.
Geological facts
Chert is so hard it can create sparks when struck against steel. It is a chemically stable rock that often resists weathering better than the surrounding limestone.
Field identification & locations
Identify in the field by its sharp, glass-like edges (conchoidal fracture) and its ability to scratch glass easily. Commonly found in nodules or beds within limestone formations.
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