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Rebecca
Gentry B.S. - University of Virginia Michael Wise, Ph.D. "This has been absolutely |
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Rebecca
Gentry B.S. - University of Virginia Michael Wise, Ph.D. "This has been absolutely |
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Determination of Crystallization History for Erongo Pegamatites, Namibia The Erongo Mountains, located in western Namibia, Africa, is a volcanic region that formed approximately 130 million years ago when the African and South American continents split apart. The Erongo Mountains are a recent area of mining for beryl and topaz crystals, many being of gemstone quality. These minerals are found in pegmatite veins and pockets within the mountains. A pegmatite is a coarse-grained granitic rock with giant crystals (up to 50 feet.) The veins are believed to occur along preexisting fractures or weak zones within the rock and the pockets are openings or void spaces within the vein that enable crystals to grow to larger than normal sizes. Individual pockets can have different chemical compositions from one another, resulting in the presence of different mineral associations. An association is a group of minerals that are found together in a rock (i.e., amethyst is associated with several varieties of quartz, muscovite, and tourmaline.) In this research, we have identified six associations within pockets of the Erongo pegmatites: amethyst, beryl, fluorite, siderite, topaz, and tourmaline. With these associations identified, we used each mineral’s spatial relationships with one another to determine the growth history of each association (i.e., which mineral grew 1st, 2nd, 3rd, etc.). Finally, in examining the mineral associations and the growth history, we were able to conclude that the chemical composition in the pegmatite pocket evolved over time. This research was supported by a grant from the National Science Foundation Research Experiences for Teachers Award Number EEC-973148, Supplement #11. |