sedimentary
Chert / Chalcedony Pebble
Cryptocrystalline Quartz (SiO2)
Hardness 6.5 to 7 on the Mohs scale, waxy to sub-vitreous luster, smooth to conchoidal fracture, fine-grained microcrystalline texture, yellowish-brown to grayish color tone.
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Physical properties
Hardness 6.5 to 7 on the Mohs scale, waxy to sub-vitreous luster, smooth to conchoidal fracture, fine-grained microcrystalline texture, yellowish-brown to grayish color tone.
Formation & geological history
Formed through the precipitation of silica-rich fluids or accumulation of siliceous organism remains (like radiolarians or diatoms) in marine or groundwater environments, followed by natural erosion into a pebble.
Uses & applications
Historically used for flintknapping into arrowheads, scrapers, and fire-starting tools. Today, smooth pebbles are used in landscaping, aquariums, and rock tumbling.
Geological facts
Chert and chalcedony are composed of microscopic quartz crystals. Due to its microcrystalline structure, chert fractures with sharp edges, making it essential for ancient toolmaking.
Field identification & locations
Identify by testing its hardness (scratches glass), waxy feel, and smooth conchoidal fracture surfaces. Commonly found along riverbeds, gravel pits, lakeshores, and exposed sedimentary rock formations.
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