mineral
Chalcedony (probably agate or common quartz)
Microcrystalline quartz, SiO₂
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray-white with tan/orange iron staining, waxy to vitreous luster, no cleavage, and conchoidal fracture. The rough, massive texture and cloudy translucence are typical of chalcedony rather than a well-formed crystal.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray-white with tan/orange iron staining, waxy to vitreous luster, no cleavage, and conchoidal fracture. The rough, massive texture and cloudy translucence are typical of chalcedony rather than a well-formed crystal.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating cryptocrystalline quartz; iron oxides create the brown-orange colors. Individual pieces may range from relatively young weathering deposits to Paleozoic or younger volcanic-hosted material.
Uses & applications
Used for cabochons, carvings, beads, lapidary specimens, and occasionally construction aggregate. Ordinary rough material generally has modest collecting value.
Geological facts
Chalcedony is quartz whose crystals are too small to see unaided; agate is a banded variety, while jasper is more opaque and impurity-rich. This specimen may be a brecciated or iron-stained chalcedony/agate fragment.
Field identification & locations
Identify by its waxy translucence, hardness, lack of cleavage, and shell-like fracture; it should scratch glass but not be scratched by a steel knife. Common worldwide, especially in volcanic regions; confirm with close inspection for banding or a thin-section test.
