Geode

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geode

(jē`ōd), hollow, globular rock nodule ranging in diameter from 1 to 12 in. (2.54–30.5 cm) or more. Most geodes are partly filled with mineral matter; they have a thin layer of chalcedony ("wavy" quartz) covering an inner lining of inward-projecting crystals. These spectacular crystals, generally quartz or, less often, calcite, make geodes highly prized by collectors. Geodes are formed in a cavity such as might be found inside a fossil shell buried in sediment. At the beginning, this cavity is probably filled with a concentrated salt solution. The first step in the creation of a geode is the formation along the inner cavity wall of a layer of gelatinous silica, which will eventually be transformed into the chalcedony layer. As the water surrounding the layer becomes less salty, osmosis induces migration of fluids into the cavity. This results in a buildup of pressure, causing the cavity to expand until the water inside and outside is equally salty. When the silica gel dehydrates, crystallizes to form chalcedony, and cracks, mineral-bearing water enters to slowly deposit the inward-projecting crystals. A geode measuring 26 ft (8 m) long and 6 ft (1.8 m) across was found in an old silver mine near Almería, NE Spain, in 2000. See also concretionconcretion,
mass or nodule of mineral matter, usually oval or nearly spherical in shape, and occurring in sedimentary rock. It is formed by the accumulation of mineral matter in the pore spaces of the sediment, usually around a fossil or fossil fragment acting as a nucleus.
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Geode

 

a form of natural mineral aggregate. It is represented by closed cavities in certain rocks, which are filled with cryptocrystalline or eucrystalline aggregates of minerals. Geodes may be isometric or round or have other shapes. The mineral substance in a geode is frequently deposited by layers, forming concentric zonal layers (for example, agates). Geodes may not be filled completely with minerals; in this case a hollow place remains in the middle that is usually strewn with vugs of crystals, stalactites, and so forth. They may be more than 1 m long in cross section; the minimum size of a geode is fractions of a centimeter (so-called amygdaloids).

geode

[′jē‚ōd]
(geology)
A roughly spheroidal, hollow body lined inside with inward-projecting, small crystals; found frequently in limestone beds but may occur in shale.

Geode

A family of X86-based microprocessors from AMD. Natively running Windows and Linux applications, the 32-bit Geode chips are used in embedded systems due to their low power requirements. The Geode was originally launched in 1999 by National Semiconductor, using a processor core from Cyrix after the two companies merged in 1997. In 2003, AMD acquired the Geode series. See x86 and AMD.
References in periodicals archive ?
When the Sakoany celestine occurrence was originally discovered, the geodes were dug from areas very close to the shore of the bay, where the productive zone was only a meter or two below the surface.
Religious offerings are made along with a prayer for an abundant harvest of geodes. Each miner then selects his own site to begin his pit, and keeps whatever he finds.
The celestine geodes are virtually monomineralic; unlike well-known celestine deposits in the U.S., France, Italy (Sicily), Germany and Poland, there is no associated hydrothermal calcite, aragonite, barite, quartz, sulfur or gypsum.
Noting the primitive approach to the exploitation of the deposit, Ratsimbazafy (1973) pointed out that many celestine geodes are probably missed in the productive zone by the rather random and restricted nature of the underground workings.
The perceived paragenetic sequence in the Ametista geode is:
(2) Crystallization of large amethyst crystals--quartz (I)--and calcite crystals upon the agate lining of the geode.
At the higher temperatures prevalent in the Brazilian geode, still other, unnamed factors doubtless enter the picture.
Above the "millerite zone" is the massive ledge, almost 1.5 meters in thickness, which forms a precarious overhang where collectors have mined geodes. The geodes from this massive siltstone are frequently of large diameter, and there is an overall greater volume of geodes in this layer as compared to the "millerite zone." Solid quartz nodules and geodes to 15 cm in diameter are found in equal abundance.
Of the geodes found in this layer about a third contain quartz only.
The highest units in the sequence contain fewer geodes. The lithology of these layers consists of massive siltstones in horizontal layers, along with cut-and-fill channel deposits.
The concentration of sulfide-bearing geodes from this locality is similar to a low-grade Mississippi Valley-type deposit.
Since that time, micro-loans have created billions of dollars of economic wealth in Asia, Africa and South Africa, according to the GEODE website.