The information presented here represents preliminary research as the result of ten-weeks of investigation in-residence at the National Museum of Natural History. This is not an official publication of the information.

As preliminary information, results and/or findings should not be cited as part of conclusive work. Please contact the authors first if you wish to utilize the information presented here.

RESEARCH

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 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.

To incorporate the experiences of this summer, I will develop curriculum to parallel the activities performed at the Smithsonian. As the study of pegmatites is beyond the scope of my curriculum, the students will study rock identification and the geologic environment of different rock types.

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Step 1--Mineral Identification

Erongo Pegmatites
- examine samples with naked eye for easily identifiable minerals
- use microscope to identify smaller, more obscure minerals

Classroom Rock Samples
- examine samples with naked eye for easily identifiable minerals
- use hand lense to facilitate identification of minerals

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Step 2--Mineral Associations

Erongo Pegmatites
- create a list of minerals present in each sample
- identify mineral associations

Classroom Rock Samples
- create a list of minerals present in each rock
- categorize rocks into types based on their mineralogy
- correlate hand samples with rock units in outcrop

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Step 3--History

Erongo Pegmatites
- examine mineral relationships
- determine growth sequence
- create crystallization history table

Classroom Rock Samples
- examine relationships of rock units in outcrop
- determine relative age of rock units
- create timeline for origin of rock units

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Step 4--Results

Erongo Pegmatites
- characterize pegmatite pocket mineralogy
- characterize chemical changes of melt
- write a report and summary of findings

Classroom Rock Samples
- characterize rock formation environment
- write a formal lab report
- describe the geologic history of area in essay

Instructional Resources Employed
- integration of FCPS Geosystems Indicators III and V
- utilization of computer technology in the classroom

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ENTOMOLOGY

Sarah Garrett
"An Inventory of Leafroller Species of Moths of the Great Smoky Mountains National Park"

Abstract / Summary

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