mineral

Agate Geode

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Concentric bands of grey, tan, and white; Luster: Waxy to vitreous; Crystal Structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65.

Hardness: 6
Color: Concentric bands of grey, tan, and white
Luster: Waxy to vitreous

Identified March 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities of volcanic or sedimentary rocks where silica-rich groundwater percolates and deposits microcrystalline quartz in layers over time. Typical ages range from millions to hundreds of millions of years (Cenozoic to Paleozoic).

Uses & applications

Commonly used for lapidary arts, jewelry (cabochons), ornamental bookends, decorative display pieces, and spiritual/metaphysical collecting.

Geological facts

The banding in agates is caused by rhythmic crystallization of silica. When the cavity is not completely filled, it remains hollow with a 'druzy' crystal lining, forming a geode like this specimen.

Field identification & locations

Identified in the field by its rounded exterior 'potato-like' shape and waxy, banded interior when broken. Commonly found in areas with past volcanic activity like Brazil, Mexico, and the Western United States. Collectors look for unbroken nodules that feel lighter than solid rocks of the same size.