Druzy Agate Geode Slices Gallery 1

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Druzy Agate Geode Slices Gallery 1

Geodes are more or less spherical or ovoid shaped, hollow concretions that form inside cavities in sedimentary and igneous rocks. The term geode is derived from the Greek geoides, meaning "Earthlike", a reference to their rounded shape. Geodes have long been regarded as objects of curiosity and prized for their beauty. Geodes are known from many localities around the world with some of the most prolific sources including Brazil, Mexico, Namibia and the United States.

In sedimentary rocks, the cavities in which geodes form are created by the dissolution of previously existing concretions that grew within soft, unlithified sediments. After the surrounding sediments lithified, the original concretions were dissolved and carried away by the action of acidic groundwater or hydrothermal solutions permeating the more resistant bedrock. In igneous rocks the cavities are created by gas bubbles, such as vesicles in basaltic lavas that become trapped and frozen in place as the host rock cools and solidifies.

As geologic conditions change over time, mineral laden ground water or hydrothermal solutions subsequently invade the hollow cavities and deposit minerals inside them, sometimes in the form of beautiful crystals and crystal druzes. The most common mineral found inside geodes is quartz in both crystalline and cryptocrystalline form (chalcedony, agate and jasper), followed by calcite. Other noteworthy minerals found in geodes include barite, celestite, dolomite, goethite, kaolinite, millerite, pyrite and sphalerite. The size, form and color of the crystals vary, making each geode unique. There is no easy way of telling exactly what the inside of a geode contains until it is opened by cutting or breaking. However, geodes from any given formation or locality usually have characteristic interior mineralizations.

Geodes are distinguished from other crystal-lined cavities or "vugs" typical of fissures and veins. Geodes differ from vugs in possessing an outer mineral layer, usually concentrically deposited layers of cryptocrystalline quartz, which is more resistant to weathering and decomposition than the surrounding bedrock. Complete geodes commonly weather out of bedrock exposures and accumulate in stream bottoms. Crystal-lined vugs disintegrate with the bedrock and do not weather out intact in such a manner.

GeodeSlice1 - Druzy Agate Geode Slice - $15.95

Locality: Unknown
Approximate Size: 49.0mm long x 34.4mm wide x 3.5mm thick. Please note the image at left may be larger than life to help show the fine details.
Approximate Weight: 42.0 carats