mineral

Polished agate geode slice

Quartz (SiO₂), chiefly chalcedony with drusy crystalline quartz; likely an agate geode

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; cream-tan chalcedony rim surrounding gray-white, sparkling drusy quartz and a small cavity. Waxy to vitreous luster, microcrystalline fibrous chalcedony with crystalline quartz lining; no obvious cleavage, specific gravity about 2.6.

Identified August 18, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled a gas cavity in volcanic rock, depositing concentric chalcedony and later quartz crystals. The specimen’s exact geological age and locality cannot be determined from the photograph; agates commonly form in Cenozoic volcanic flows.

Uses & applications

Used as a decorative slice, paperweight, lapidary specimen, and jewelry component; attractive drusy examples have modest collector value.

Geological facts

The banded outer material is agate, while the glittering cavity lining is drusy quartz. The apparent “crystal” center is likely quartz rather than a separate mineral.

Field identification & locations

Identify by its hard, silica-rich rind, waxy chalcedony texture, and sparkling quartz cavity; common sources include Brazil, Uruguay, Mexico, India, and the western United States. A scratch test should be avoided on polished surfaces; quartz will scratch glass.