mineral

Banded agate geode slice

Microcrystalline quartz (SiO₂), chiefly chalcedony with druzy quartz

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; gray, black, cream, and brown concentric banding with a dull-to-waxy chalcedony luster and sparkling drusy cavity. Quartz is trigonal and has no cleavage; specific gravity is about 2.6.

Identified September 14, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled cavities in volcanic rock, depositing chalcedony in successive layers and quartz crystals inside the remaining void. Most such agates formed during the Cenozoic or older volcanic episodes, depending on locality.

Uses & applications

Used as polished display pieces, cabochons, ornaments, and lapidary material; agate is also used for beads, bookends, and decorative slabs.

Geological facts

The curved bands record changing chemistry and flow conditions during mineral deposition. The specimen appears cut and polished on one face, exposing a natural druzy-lined cavity.

Field identification & locations

Identify by translucent concentric banding, very hard quartz surfaces, and a sugary quartz cavity; it commonly occurs in basaltic volcanic regions, especially Brazil, Uruguay, Mexico, and the United States. Avoid acids and harsh impacts when cleaning.