mineral
Chalcedony / Agate nodule
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness of 6.5-7 on Mohs scale; translucent amber to brownish-yellow color; waxy to dull luster; conchoidal fracture; microcrystalline/cryptocrystalline trigonal structure; specific gravity around 2.58-2.64.
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Physical properties
Hardness of 6.5-7 on Mohs scale; translucent amber to brownish-yellow color; waxy to dull luster; conchoidal fracture; microcrystalline/cryptocrystalline trigonal structure; specific gravity around 2.58-2.64.
Formation & geological history
Formed by secondary precipitation of silica from low-temperature groundwater or hydrothermal fluids filling cavities (vesicles) within volcanic basalt or sedimentary rock layers.
Uses & applications
Popular for lapidary work, cabochon cutting, jewelry, tumbling, and amateur rock collecting.
Geological facts
Natural weathering and alluvial transport often smooth the outer surface while leaving hollows, pit marks, and thin residual matrix rinds as seen on this water-worn nodule.
Field identification & locations
Identified by its waxy sheen, translucent edges when backlit, resistance to scratching by a steel nail, and irregular, cavity-filled river-worn nodule shape. Commonly found in gravel beds, river bars, and desert washes worldwide.
