sedimentary
Chert (Yellow and Red Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Banded yellow, orange, and reddish-brown, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Banded yellow, orange, and reddish-brown, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. The colors are derived from iron oxide impurities (limonite for yellow, hematite for red) during mineralization.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp conchoidal fracture. Today used for landscaping, tumbled stones, jewelry cabochons, and as a collector's specimen.
Geological facts
Chert and Jasper have been used by humans for over a million years. It is one of the most durable sedimentary rocks and can survive long-distance transport in rivers and glacial till.
Field identification & locations
Identify in the field by its hardness (it can scratch glass) and its smooth, shell-like (conchoidal) breaking pattern. Common in riverbeds, gravel pits, and sedimentary outcrops worldwide.
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