mineral
Polished dendritic agate or jasper pebble
Microcrystalline quartz (chalcedony), SiO₂, with dark manganese-oxide inclusions
AI-generated identification · may be incorrectSmooth polished, elongated pebble with cream-tan chalcedony and dark gray-black dendritic or mossy zones; vitreous to waxy luster, no visible cleavage, conchoidal fracture, and Mohs hardness about 6.5–7. Specific gravity is approximately 2.58–2.65.
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Physical properties
Smooth polished, elongated pebble with cream-tan chalcedony and dark gray-black dendritic or mossy zones; vitreous to waxy luster, no visible cleavage, conchoidal fracture, and Mohs hardness about 6.5–7. Specific gravity is approximately 2.58–2.65.
Formation & geological history
Silica-rich groundwater filled cavities or fractures in volcanic rock, while manganese oxides formed branching dark inclusions during deposition. Chalcedony deposits are commonly Cenozoic to older, but the specimen’s exact age cannot be determined visually.
Uses & applications
Used as a cabochon, tumbled stone, ornamental object, and lapidary material; attractive examples have modest jewelry and collector value.
Geological facts
The dark pattern may be dendritic agate, moss agate, or jasper rather than true banded agate; polished surfaces can make these varieties difficult to separate from a photograph.
Field identification & locations
Look for waxy luster, translucency at thin edges, hardness sufficient to scratch glass, and irregular branching inclusions rather than metallic color. Common sources include India, Madagascar, Brazil, Uruguay, and the western United States.
