March Speaker: "Pegmatites: Earth's Most Amazing Rocks" by Dr. Mike Wise from the Smithsonian's Department of Mineral Sciences

by Cindy Schmidtlein, MSDC Vice President

Dr. Mike Wise, Geologist, Smithsonian National Museum of Natural History, Department of Mineral Sciences. Photo from the Smithsonian

Our speaker for our March meeting is Dr. Mike Wise from the Department of Mineral Sciences at the Smithsonian's National Museum of Natural History (NMNH). Dr. Wise got his Ph.D. from the University of Manitoba in 1987 and is a prolific author and speaker that recently included a presentation at the 42nd Annual Tucson Mineral Symposium at the Tucson Convention Center. We are truly fortunate that Mike will talk to us about his favorite topic: "Pegmatites: Earth's Most Amazing Rocks."

The global exploitation of granitic pegmatites (exceptionally coarse to gigantic-grained igneous rocks) as major sources of industrial, technological and gemological materials, require that we have a strong understanding of the processes that generate them.

Pegmatites are important sources of rare-elements, and when present in economic quantities, these elements may be extracted for use in a wide range of technological applications. Some of the world's best-known gem materials (e.g., aquamarine, emerald, sapphire, topaz, and tourmaline) and mineral specimens are obtained from pegmatite deposits.

Dr. Wise's research in the Department of Mineral Sciences focuses on three broad, but closely linked, disciplines which are the basic research components necessary for a full understanding of the pegmatite-generating process.

Crystal chemistry and crystal structures of pegmatite minerals

Basic mineralogical studies carried out on major and accessory pegmatite minerals include: the solution and refinement of crystal structures, investigation of structural states (e.g., order-disorder) in minerals, and the effects of "pegmatophile" elements (e.g., Rb, Cs, Li, B) on mineral structures.

Petrology and geochemistry of pegmatites 

Petrographic study of pegmatite textures is fundamental to understanding the nucleation and growth of giant crystals. Multi-generations of tourmalines, feldspars, micas, garnets, and Nb-Ta oxide minerals are typical of many chemically evolved pegmatites and the minor and trace element signatures of these minerals help to decipher changes in melt and fluid composition during pegmatite consolidation.

Evolution of granite-pegmatite systems

Field-based studies of the internal zoning of individual pegmatites, the regional zonation of granite-pegmatite systems and the global relationship between pegmatites and broad geologic and tectonic settings helps provide a better understanding of the processes responsible for pegmatite generation and can provide important information on the chemical evolution of the earth's crust.