sedimentary
Chert (Nodule/Common Chert)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan to light grey with tan patina, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan to light grey with tan patina, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds, often during the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads); currently used in road construction, as an abrasive, and sometimes in landscaping.
Geological facts
Chert is so hard it can create sparks when struck against steel. It was one of the most vital materials for prehistoric humans due to its ability to hold a sharp edge.
Field identification & locations
Identify by its waxy luster, conchoidal (shell-like) fracture, and the fact it can scratch steel or glass. Commonly found as nodules in limestone outcrops or as river stones.
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Brecciated Chert (Microcrystalline Silica)
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