sedimentary

Fairburn Agate / Agate-bearing Breccia

Cryptocrystalline Quartz (SiO2) within Jasper/Breccia matrix

Hardness: 6.5 - 7 (Mohs scale); Color: Vibrant reds, whites, and yellows with concentric 'fortification' banding; Luster: Vitreous to waxy; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture).

Hardness: 6
Luster: Vitreous to waxy

Identified January 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich groundwater into cavities (vugs) within limestone of the Pennsylvanian-Permian age (approx. 250-300 million years ago), later weathered out and redeposited as alluvial gravels during the Tertiary period.

Uses & applications

Primarily used as a gemstone for jewelry (cabochons), as high-end collectable specimens, and for lapidary lapidary polishing. It is the State Gemstone of South Dakota.

Geological facts

Fairburn agates are famous for their unique 'holly-leaf' or sharp-angled fortification banding patterns. Unlike many agates found inside lava rocks, these originated in sedimentary limestone formations.

Field identification & locations

Identify in the field by looking for the tell-tale 'holly-leaf' banding and vibrant red or orange hues on weathered surfaces. Primarily found in the Fairburn Agate Beds of Custer County and the Buffalo Gap National Grasslands in South Dakota, USA.

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