mineral
Chalcedony / Chert Pebble
Silicon Dioxide (SiO2) - Microcrystalline Quartz
AI-generated identification · may be incorrectMohs hardness of 6.5-7; waxy to dull luster; translucent to opaque brownish-tan body color; conchoidal fracture; trigonal microcrystalline structure; specific gravity ~2.58-2.64.
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Physical properties
Mohs hardness of 6.5-7; waxy to dull luster; translucent to opaque brownish-tan body color; conchoidal fracture; trigonal microcrystalline structure; specific gravity ~2.58-2.64.
Formation & geological history
Formed through low-temperature precipitation of silica-rich groundwater within cavities of sedimentary or volcanic rocks, subsequently weathered out and smoothed by fluvial or glacial transport.
Uses & applications
Historically used for knapping stone tools, arrowheads, and fire-striking; currently popular for lapidary tumbling, polishing, carving, and mineral collecting.
Geological facts
Chalcedony is the cryptocrystalline variety of quartz; when banded it is called agate, and when dark and opaque it is commonly referred to as flint or chert.
Field identification & locations
Identifiable in gravel beds and rivers by its waxy sheen, smooth rounded surfaces from water erosion, conchoidal fracture marks, and ability to easily scratch glass.
