mineral

Quartz Geode

Silicon Dioxide (SiO₂)

Hardness: 7 on the Mohs scale; Color: White to colorless, often with iron staining (yellow/brown); Luster: Vitreous (glassy); Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: White to colorless, often with iron staining (yellow/brown)
Luster: Vitreous (glassy)

Identified March 30, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities within volcanic or sedimentary rocks. Over millions of years, mineral-rich groundwater seeps into these hollow voids, precipitating silica layers that grow inward to form crystals. They can range from millions to hundreds of millions of years in age.

Uses & applications

Primarily used as decorative display pieces, for geological education, and in metaphysical collecting. Crushed quartz is also used in industry for glass making and abrasives.

Geological facts

Geodes are often referred to as 'thunder eggs' in some regions. While they look like ordinary rocks on the outside, their hollow interiors can contain a variety of minerals including amethyst, citrine, or calcite alongside the primary quartz.

Field identification & locations

Identify in the field by looking for rounded, lumpy nodules that feel lighter than they look (indicating a hollow center). Common locations include the American Midwest (Keokuk geodes), Brazil, and Morocco. Tap the specimen gently; quartz will sound different than solid limestone or basalt.