mineral
Polished dendritic agate or jasper
Microcrystalline quartz (SiO₂), likely chalcedony with iron/manganese dendrites
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; glossy vitreous-to-waxy luster, opaque dark brown/black body with a pale gray-white central area and possible brown dendritic inclusions. It is cryptocrystalline, lacks visible cleavage, and typically has specific gravity near 2.6.
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Physical properties
Hardness about 6.5–7 Mohs; glossy vitreous-to-waxy luster, opaque dark brown/black body with a pale gray-white central area and possible brown dendritic inclusions. It is cryptocrystalline, lacks visible cleavage, and typically has specific gravity near 2.6.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rock; contrasting dendrites develop from manganese or iron oxides. The specimen is polished, so its exact geological age and locality cannot be determined from the image.
Uses & applications
Used as a lapidary stone for cabochons, tumbled stones, carvings, and jewelry; valued mainly for pattern and polish rather than industrial use.
Geological facts
Dendritic patterns are mineral-growth inclusions, not plant fossils. The dark host could also be jasper or black chalcedony, and identification would be improved by examining translucency and testing hardness.
Field identification & locations
Commonly found in volcanic terrains, including India, Madagascar, Brazil, Uruguay, Mexico, and the western United States. A glassy polish, lack of cleavage, waxy fracture, and inability to scratch it with a steel knife support chalcedony; avoid confusing it with man-made glass.
