mineral

Polished botryoidal agate/geode fragment

Microcrystalline quartz (SiO₂), likely chalcedony with druzy quartz

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray, white, and dark purple-brown banding with a glassy to waxy luster and sparkly druzy surface. It has cryptocrystalline quartz structure, no prominent cleavage, and typical specific gravity near 2.6.

Identified September 13, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled cavities in volcanic rock, depositing layered chalcedony and later quartz crystals. Such agates commonly formed during the Cenozoic or earlier volcanic episodes, but the specimen’s exact age and locality cannot be determined from the image.

Uses & applications

Used for cabochons, jewelry, ornaments, polished slices, and mineral collecting; attractive specimens generally have modest decorative value.

Geological facts

The rounded, cauliflower-like texture is called botryoidal. Dark coloration may reflect iron or manganese oxides, and the glossy appearance suggests polishing or a natural weathered surface.

Field identification & locations

Identify it by concentric or irregular chalcedony banding, very high hardness, and inability to scratch with a steel knife easily; a streak test is white. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States.