Great South Gems & Minerals

• Geode, Matched Halves • 
(Brazil)

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• Geode, Matched Halves • 

Geodes

Small geodes that have been cut open with a diamond saw to show the beautiful crystals inside. These are from Brazil. The price is for the two matching halves. The cut face of the geode has a super polish to show off the agate around the outer edges. These make a good object lesson...ugly on the outside, beautiful on the inside.

Geodes are rock formations which occur in sedimentary and certain volcanic rocks. They are normally spherical in shape and has a cavity, or vug, in which internal crystal formations or concentric banding. The exterior of the most common geodes is generally limestone or a related rock, while the interior contains silica, or quartz crystals and/or chalcedony. Other geodes are completely filled with crystals, being solid all the way through. These types of geodes are called nodules. The only difference between a geode and a nodule is that a geode has a hollow cavity, and a nodule is solid.
See: en.wikipedia.org/wiki/Geode
www.igsb.uiowa.edu/browse/geodes/geodes.htm

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Geodes begin as bubbles in volcanic rock or as animal burrows, tree roots or mud balls in sedimentary rock. Over time, the outer shell of the spherical shape hardens, and water containing silica precipitation forms on the inside walls of the hollow cavity within the geode. The silica precipitation can contain any variety of dissolved minerals, the most common being quartz, but amethyst and calcite are also found. Occasionally, and rarely, a geode if found to contain the original water still trapped within. These rarities are called enhydros.

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See our links to other geodes:
www.greatsouth.net/minerals/p-M134.html
www.greatsouth.net/minerals/p-M248.html

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