Quartz Geode

Physical Properties

Hardness: 7 (Mohs scale); Color: Clear to white; Luster: Vitreous (glassy); Crystal Structure: Hexagonal; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed as secondary precipitation within hollow cavities in sedimentary or volcanic rocks. Mineral-rich groundwater seeps into the hollows, and over thousands of years, crystals grow inward toward the center.

Uses & Applications

Commonly used for ornamental purposes, home decor, collector specimens, and educational kits for children. Small specimens are often used in lapidary work.

Geological Facts

Geodes are often referred to as 'thunder eggs' in certain regions. While they look like ordinary rounded rocks from the outside, the interior cavity can contain various minerals, with quartz and amethyst being the most common.

Field Identification & Locations

Identify in the field by looking for rounded, lumpy nodules that feel lighter than they look (suggesting a hollow interior). Common in limestone or volcanic ash deposits in locations like Missouri, Mexico, and Brazil.

Identified on: 4/27/2026

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