sedimentary

Quartz Geode

Quartz (Silicon Dioxide - SiO2) within a Chalcedony and Limonite shell

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Clear to milky white internal crystals, grey or brown outer rind; Luster: Vitreous (glassy) inside, dull/earthy outside; Crystal Structure: Hexagonal (inside); Cleavage: None/Conchoidal; Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Luster: Vitreous (glassy) inside, dull/earthy outside

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in hollow cavities within sedimentary rocks (typically limestone) or volcanic ash. Mineral-rich groundwater seeps into these cavities over millions of years, precipitating layers of silica that crystallize into quartz. This specimen likely dates from the Carboniferous to Eocene periods depending on exact locality.

Uses & applications

Primarily used for decorative purposes, geological education, metaphysical collecting, and jewelry lapidary. Smaller geodes are often sold as 'break-your-own' kits for hobbyists.

Geological facts

Geodes are often referred to as 'Earth Eggs.' While they look like ordinary round stones from the outside, they contain hollow cavities lined with crystals. One of the largest geode sites in the world is the 'Geode Cave' in Ohio, but most commercial specimens like this one come from Morocco or the Mid-Western US.

Field identification & locations

Identify in the field by looking for rounded, lumpy, cauliflower-like rock nodules that are surprisingly light for their size (indicating a hollow center). Common locations include Keokuk, Iowa; Tabasco, Mexico; and Ouarzazate, Morocco. Collectors should look for a high ratio of clear crystals to host rock.