What Is a Geode?
A geode is a rock with a hollow formation lined with crystals or mineral layers inside. On the outside, a geode looks like a rough, ordinary stone but when opened, it reveals sparkling quartz, amethyst, calcite, or other stunning minerals.
How Do Geodes Form?
Geodes form when cavities or bubbles in volcanic or sedimentary rock fill with mineral-rich water. As the water evaporates or cools, crystals slowly grow along the inner walls, creating nature’s very own hidden treasure.
Popular Types of Geodes
Not all geodes are the same! Their shape, size, and sparkle depend on where they form and what minerals are present during their formation. This is by no means an exhaustive list of geodes. There are too many to name with new types being found all the time.
Here are some of the most popular types of geodes found today:
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Las Choyas Geodes (“Coconut Geodes”): From Chihuahua, Mexico. Usually round with walls made up of blue to gray chalcedony or brown siderite. The most dominate crystals inside are quartz (clear, smokey or amethyst) and calcite.
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Trancas Geodes: Another geode from Chihuahua, Mexican. Often filled with scepter quartz, chalcedony bands, sparkling drusy quartz, and other unusual quartz projections.
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Oco Geodes: Small but mighty Brazilian geodes. These geodes often make good jewelry.
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Keokuk Geodes: A sedimentary geode from Iowa. The dominating crystals are quartz and calcite.
Minerals Commonly Found Inside Geodes
Opening a geode is like unwrapping a mystery gift — you never know what’s inside until you look. The most common geode minerals include:
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Quartz: The most common geode mineral, appearing as clear, smoky, or amethyst.
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Chalcedony: Smooth, banded quartz that often lines the walls of a geode.
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Calcite: Sharp, distinct crystals in shades of white, yellow, or honey.
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Amethyst: A purple variety of quartz, beloved by collectors.
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Agate: Concentric bands of colorful chalcedony, sometimes framing crystals.
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Pyrite (“Fool’s Gold”): Adds metallic sparkle to a geode’s interior.
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Celestite: Sky-blue crystals found in some Ohio and Madagascar geodes.
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Goethite: A black to brownish, red or orange mineral that often forms needle-like bladed crystals.
- Hematite: A metallic to earthy mineral, usually red, gray, or black, forming spheres and rosettes.
Where Are Geodes Found?
Geodes are discovered all over the world, but some locations are especially well-known:
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Mexico: Las Choyas and Trancas geodes.
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Brazil & Uruguay: Famous for large amethyst and agate geodes.
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United States: Dugway geodes in Utah, Keokuk geodes in Iowa/Missouri/Illinois, and celestite geodes in Ohio.
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Morocco & Madagascar: Known for a wide variety of geodes with unique crystals.
Why Collect Geodes?
Because they're cool! Seriously though, geodes aren’t just pretty rocks, they’re natural mystery balls. Each geode is one of a kind. Whether you’re a collector, a rockhound, or just curious about Earth’s hidden wonders, geodes are proof that beauty often lies beneath the surface.
