sedimentary
Chert (Red Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: Reddish-brown (due to iron oxides), Luster: Dull to waxy, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 Mohs, Color: Reddish-brown (due to iron oxides), Luster: Dull to waxy, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed in deep-water sedimentary environments from the accumulation of siliceous remains of microscopic organisms like radiolaria or through chemical precipitation in hydrothermal veins.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include jewelry (lapidary), decorative stones, and as an abrasive in some industrial processes.
Geological facts
Chert is one of the hardest commonly found sedimentary rocks and can strike sparks against steel. Red varieties are often called Jasper when they are opaque and rich in iron.
Field identification & locations
Identify by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass easily. Found globally in limestone beds or as nodules in river beds.
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