sedimentary
Chert (Common Opal/Jasper variety)
Microcrystalline Quartz (SiO2)
Mohs hardness of 6.5-7; olive green to grayish color; waxy to vitreous luster; cryptocrystalline structure; prominent conchoidal (shell-like) fracture; specific gravity 2.6-2.7.
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Physical properties
Mohs hardness of 6.5-7; olive green to grayish color; waxy to vitreous luster; cryptocrystalline structure; prominent conchoidal (shell-like) fracture; specific gravity 2.6-2.7.
Formation & geological history
Formed via the accumulation of siliceous remains of diatoms or radiolarians, or through chemical precipitation in hydrothermal or groundwater environments. This specimen shows signs of river or coastal tumbling (water-worn).
Uses & applications
Historically used for making stone tools due to its sharp edges when broken; currently used for lapidary work, jewelry (cabochons), and as a collector's specimen.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded. Some varieties with high iron content are called jasper, while translucent varieties are often called chalcedony.
Field identification & locations
Identified in the field by its smooth, waxy texture and sharp, curved fracture patterns. Commonly found in riverbeds, glacial till, and coastal areas.
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