mineral

Agate (Fortification Agate)

Banded Chalcedony (SiO2)

Hardness: 6.5-7. Color: White, cream, and tan with distinct banding. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.64.

Hardness: 6
Color: White, cream, and tan with distinct banding
Luster: Waxy to vitreous

Identified April 11, 2026More mineral →

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Physical properties

Hardness: 6.5-7. Color: White, cream, and tan with distinct banding. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.64.

Formation & geological history

Formed as a secondary mineral in the cavities (vesicles) of volcanic rocks (igneous) through the deposition of silica-rich groundwater. The layers form sequentially over thousands of years.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), or as a collector's specimen. Known for being durable and taking a high polish.

Geological facts

The 'V-shaped' lines visible in this specimen are known as 'fortification' banding because they resemble the floor plans of old star-shaped fortresses. Agate has been used for ornaments since Ancient Greek times.

Field identification & locations

Identify by looking for translucent edges, waxy luster, and concentric or angular banding. This specimen appears to be a fragment showing a conchoidal fracture. Commonly found in riverbeds or volcanic outcrop areas.

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