sedimentary
Chert (Chalcedony)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Tan with dark brown/black manganese oxide or organic staining, Luster: Waxy to vitreous when wet, Structure: Microcrystalline, Cleavage: None (conchoidal fracture).
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Physical properties
Hardness: 7 (Mohs), Color: Tan with dark brown/black manganese oxide or organic staining, Luster: Waxy to vitreous when wet, Structure: Microcrystalline, Cleavage: None (conchoidal fracture).
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids in sedimentary environments. Common in marine deposits where silica from diatoms or radiolarians replaces limestone or accumulates as nodules.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for decorative gravel, landscaping, and lapidary tumbling.
Geological facts
This specimen displays a distinct waxy luster and smooth, rounded water-worn texture. The dark coating is likely desert varnish or manganese staining common in river-worn specimens.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and its smooth, waxy surface. It is ubiquitously found in riverbeds and gravel pits throughout North America.
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