sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: dull green, brown, and reddish-tan, Luster: dull to waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), SG: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: dull green, brown, and reddish-tan, Luster: dull to waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), SG: 2.6-2.7
Formation & geological history
Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). This specimen appears to be a river-worn pebble.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative landscaping stone or as a base for construction.
Geological facts
Chert is essentially the same mineral as flint, though flint is typically used for darker, chalk-hosted varieties. It is extremely durable and chemical resistant.
Field identification & locations
Identified in the field by its hardness (it will scratch glass), its conchoidal (shell-like) fracture, and its smooth, waxy feel when freshly broken. Very common in riverbeds.
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