mineral
Agate (Geode nodule)
Cryptocrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 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 More mineral →
Explore Agate (Geode nodule) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
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
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.
