
Amethyst Geode

by Tikvah's Hope
Title
Amethyst Geode
Artist
Tikvah's Hope
Medium
Photograph - Photograph
Description
Amethyst is a well known mineral and gemstone. It is the purple variety of the mineral Quartz, and its most valuable and prized variety. Its name derives from the Greek "amethystos", which means "not drunken", as Amethyst in antiquity was thought to ward off drunkenness. The color of some Amethyst specimens from certain localities slowly fade upon prolonged exposure to light. When used as a gemstone, Amethyst is often heat treated to deepen the color, or to transform it into Citrine. Some varieties may also change to a light green color, which is given the trade name "Prasiolite", or "Green Amethyst", as it is more commonly known in the gem trade.
Geodes are usually formed in �bubbles� and other cavities in volcanic rock, especially molten rock that has intruded into other preexisting rock layers. (They can also form in surface lava flows that are thick enough so that cooling is slow.) After an intrusion of molten rock is in place, it gradually cools and hardens. Various minerals crystallize out at different temperatures so that part of the intrusion is still liquid while other parts have already solidified. Molten rock also contains large amounts of dissolved gases. As the rock cools, these gases come out of solution and form �bubbles� and cavities in the rock.
Amethyst is most prevalent as small stubby pyramidal crystals, although several localities such as the Mexican occurrences are well-known for producing elegantly tall prismatic crystals, which are very highly regarded by collectors. Amethyst also forms the internal lining of geodes, some of which can be over 10 feet tall and weighing several tons.
Uploaded
January 10th, 2013
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