sedimentary
Chert Nodule / Flint
Microcrystalline Quartz (SiO2)
Mohs hardness 7, dull to earthy luster on rough exterior, subconchoidal fracture, yellowish-brown to tan earthy exterior, very fine microcrystalline grain structure.
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Physical properties
Mohs hardness 7, dull to earthy luster on rough exterior, subconchoidal fracture, yellowish-brown to tan earthy exterior, very fine microcrystalline grain structure.
Formation & geological history
Formed in sedimentary rock layers, primarily limestone or chalk, through biochemical precipitation of silica or groundwater alteration of calcium carbonate.
Uses & applications
Historically used for stone tools and fire-starting. Today used in road construction, landscape stone, and by rockhounding enthusiasts for lapidary work.
Geological facts
Chert nodules often form around organic material on the ancient seafloor. When cracked open, they may reveal bands of different colors or hollow geode centers lined with quartz crystals.
Field identification & locations
Can be identified by its rounded nodular shape, smooth texture when chipped, high hardness (scratches steel and glass), and dull weathering rind. Widely found in limestone formations worldwide.
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