Research Training Program

Madison Barkley
Mount Holyoke College
South Hadley, Massachusetts

Mike Wise, Ph.D.
Supervising Scientist
Department of Mineral Sciences

"Through the RTP program, I have developed a new level of appreciation and respect for the amount of hard work and perseverance needed to become a research scientist and for the scientific process. "

Fluorine content and temperature effects
on the crystal structure of pegmatitic topaz

Granitic pegmatites are large grained rocks that formed from molten rock (melt) within the earth's crust. Water, plus the elements fluorine, boron, and phosphorous, causes the melt to harden at lower temperatures and helps the formation of large crystals. There are two chemical types of granitic pegmatites, LCT and NYF. LCT pegmatites are rich in the elements lithium, cesium, and tantalum and are usually associated with mountain building events. NYF pegmatites enriched in the elements niobium and yttrium and are related to thinning of the earth's crust. NYF pegmatites are particularly rich in fluorine and the fluorine-rich mineral topaz whereas LCT pegmatites typically have low fluorine contents and topaz is generally uncommon. This project examined changes in the crystal structure of topaz using X-ray diffraction and electron microprobe analysis. The shape of the topaz crystal structure resembles a shoebox with the changes in the topaz structure corresponding to changes in the height, width, and length of the shoebox. The data shows different degrees of structural changes due to fluorine content in NYF topaz relative to LCT topaz. Heating the topaz to 1300o Fahrenheit causes the crystal structure of topaz to shrink.

This research was supported by the Smithsonian Women's Committee Endowment.

Letter of gratitude