mineral

Agate (Geode nodule)

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: White and butterscotch center with dark brown outer band; Luster: Vitreous/Waxy; Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: White and butterscotch center with dark brown outer band
Luster: Vitreous/Waxy

Identified March 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities of volcanic or metamorphic rocks when silica-rich groundwater precipitates over long geological periods (Cenozoic to Mesozoic era roughly). Layering occurs from different mineral impurities over time.

Uses & applications

Commonly used in jewelry (cabochons), lapidary art, watch bearings, and as decorative collector pieces or paperweights.

Geological facts

The banding in agates is often rhythmic, caused by the change in chemical concentration of the fluid as it fills the rock cavity. Some are called 'Thunder Eggs' when they look like common rocks on the outside but contain hidden crystals.

Field identification & locations

Identify by the distinct translucent waxy center and concentric or solid banding inside a rough, weathered exterior shell. Often found in riverbeds or volcanic ash deposits in Brazil, Uruguay, and the US Northwest.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

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Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

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Epidote

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