mineral
Chalcedony (likely yellow agate or jasper fragment)
Microcrystalline quartz, SiO₂
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; waxy to dull luster; translucent cream-yellow color with rusty staining; cryptocrystalline quartz, lacking visible cleavage and commonly showing conchoidal fracture. The flaked edges suggest it may be a worked or naturally fractured piece.
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Physical properties
Hardness 6.5–7 Mohs; waxy to dull luster; translucent cream-yellow color with rusty staining; cryptocrystalline quartz, lacking visible cleavage and commonly showing conchoidal fracture. The flaked edges suggest it may be a worked or naturally fractured piece.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures, commonly in volcanic rocks; iron impurities create yellow to brown colors. Most specimens formed during relatively young volcanic episodes, though age depends on locality.
Uses & applications
Used for carvings, cabochons, beads, lapidary tools, and decorative stone; this small rough fragment has mainly teaching or modest collecting value.
Geological facts
Chalcedony is quartz whose crystals are too small to see individually; agate is banded chalcedony, while jasper is opaque and impurity-rich.
Field identification & locations
Test by its glassy/conchoidal fracture and resistance to scratching; it should not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, Madagascar, and volcanic regions worldwide.
