sedimentary
Chert (with Iron Oxide / Jasperoid Layering)
Microcrystalline Quartz (SiO2)
Hardness 7 on Mohs scale; dull to waxy luster; conchoidal to uneven fracture; microcrystalline structure; shades of tan, yellow, cream, and reddish-brown due to iron oxide inclusions.
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Physical properties
Hardness 7 on Mohs scale; dull to waxy luster; conchoidal to uneven fracture; microcrystalline structure; shades of tan, yellow, cream, and reddish-brown due to iron oxide inclusions.
Formation & geological history
Formed by the precipitation of silica-rich fluids in sedimentary rock environments, or from the accumulation of siliceous organism remains (like radiolarians and diatoms) on oceanic floor beds.
Uses & applications
Historically used for knapping stone tools and arrowheads. Modern uses include aggregate in construction, landscaping stones, and lapidary tumbling for hobbyists.
Geological facts
Chert was one of the most critical raw materials for prehistoric humans due to its sharp edges when broken (conchoidal fracture). Varieties rich in iron oxide are often called jasper.
Field identification & locations
Identified in the field by its hardness (scratches glass readily), smooth to slightly grainy texture, sharp edges when broken, and lack of reaction to dilute acid. Common in limestone and chalk formations worldwide.
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