mineral

Banded Agate Geode (with Microcrystalline Quartz)

Silicon Dioxide (SiO2) - variety Chalcedony/Agate

Hardness: 6.5-7 (Mohs scale); Color: Multicolored concentric bands of grey, tan, and white with a translucent white center; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.60-2.65

Hardness: 6
Luster: Waxy to vitreous

Identified March 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich groundwater into voids or cavities within igneous host rocks (typically basalt or rhyolite). This specimen features a 'geode' center where crystallization was incomplete, leaving a hollow or crystalline druzy core.

Uses & applications

Used extensively in gemstone jewelry (cabochons), ornamental decoration, bookends, and as metaphysical stone specimens. Historically used for making mortars and pestles due to hardness.

Geological facts

The banding in agate is caused by the rhythmic precipitation of silica over long periods of time. This specific specimen displays 'fortification' banding, so named because the sharp angles resemble the bastions of medieval fortresses.

Field identification & locations

Identify in the field by looking for rounded, waxy-textured nodules with a rough, weathered outer 'rind'. Common locations include Brazil, Uruguay, Lake Superior (USA), and India. Collectors should look for distinct, high-contrast banding and clear central crystals.

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