mineral
Tumbled brown chalcedony or quartzite pebble
Microcrystalline quartz (SiO₂), likely chalcedony; exact identification requires testing
AI-generated identification · may be incorrectTypically Mohs hardness 6.5–7, vitreous to waxy luster, opaque to translucent brown coloration, and no visible cleavage; specific gravity about 2.6. The smooth rounded surface indicates water-worn or mechanically tumbled material.
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Physical properties
Typically Mohs hardness 6.5–7, vitreous to waxy luster, opaque to translucent brown coloration, and no visible cleavage; specific gravity about 2.6. The smooth rounded surface indicates water-worn or mechanically tumbled material.
Formation & geological history
Chalcedony forms when silica-rich groundwater fills cavities and fractures, while quartzite forms by metamorphism of sandstone; either may be Precambrian to recent in age. The specimen was likely rounded naturally or in a tumbler.
Uses & applications
Commonly used for lapidary cabochons, carvings, beads, and inexpensive decorative stone; usually has limited commercial value unless it displays unusual color or pattern.
Geological facts
Brown coloration can result from iron oxides, organic impurities, or weathering. The image alone cannot reliably distinguish chalcedony from jasper, quartzite, or another brown quartz-rich rock.
Field identification & locations
Look for quartz-like hardness: it should scratch ordinary glass but not be scratched by a steel knife; chalcedony commonly shows a waxy, smooth fracture rather than cleavage. Common sources include river gravels and silica-rich volcanic regions.
