sedimentary

Blue Grey Agate Geode

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Pale blue to smoky grey interior with a tan/brown exterior matrix; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture.

Hardness: 6
Luster: Waxy to vitreous

Identified July 21, 2026More sedimentary →

Explore Blue Grey Agate Geode in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed by the deposition of silica from groundwater into cavities (vesicles) within volcanic or sedimentary rocks across millions of years. This specimen shows a solid chalcedony fill with a weathered outer rind.

Uses & applications

Commonly used in lapidary arts for bookends, coasters, jewelry cabochons, and as decorative display specimens for collectors.

Geological facts

Agates often form in concentric bands; this specific specimen is more characteristic of a solid chalcedony nodule. The blue-grey color is often a result of the Tyndall effect, where minute particles scatter light.

Field identification & locations

Identify in the field by looking for rounded, potato-like nodules with a rough, waxy skin. They are commonly found in Brazil, Uruguay, and the western United States. Breaking or cutting them reveals the hidden crystal interiors.