sedimentary
Geode (Unopened)
SiO2 (Quartz-filled Sedimentary Nodule)
Hardness: 7 (inner quartz), Color: Ocher, brownish-grey exterior, Luster: Dull/earthy exterior, Crystal structure: Trigonal (internal), SG: 2.6-2.7. It has a rough, pitted cauliflower-like texture.
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Physical properties
Hardness: 7 (inner quartz), Color: Ocher, brownish-grey exterior, Luster: Dull/earthy exterior, Crystal structure: Trigonal (internal), SG: 2.6-2.7. It has a rough, pitted cauliflower-like texture.
Formation & geological history
Formed via the precipitation of minerals into internal cavities of sedimentary rocks (like limestone) or volcanic ash. These cavities are often created by gas bubbles or decaying organic matter over millions of years.
Uses & applications
Primarily for mineral collecting, education, and as decorative lapidary items once cut and polished to reveal the crystal interior.
Geological facts
The word 'Geode' comes from the Greek word 'Geoides' meaning earth-like. Some geodes are 'thunder eggs' which are solid, while true geodes must have a hollow interior.
Field identification & locations
Identify in the field by their rounded, bumpy 'cauliflower' exterior and they often feel lighter than a solid rock of the same size. Commonly found in desert regions or limestone beds.
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