SCANNING ELECTRON MICROSCOPE STUDY OF TOURMALINE FROM PEGMATITES IN THE SOUTHEASTERN UNITED STATES

Tourmaline crystals collected from two different localities in the Southeast show similarities in composition despite substantial differences in size as well as differences in the composition of the host pegmatite from which they were extracted. The suite of samples collected from Spruce Pine in North Carolina are from the border zone of a pegmatite composed of quartz, feldspar, mica, and garnet. The crystals here are very small but numerous and are intermixed with biotite. The samples collected from the Hogg Mine in Lagrange, Georgia are contained within a well zoned but deeply weathered pegmatite with a quartz core and kaolinite from altered feldspar. These crystals are in some cases relatively large with well defined crystal symmetry, and contain numerous micro fractures. At first glance, all of these crystals were believed to be Fe end member schorl, but after further analysis under the SEM all crystals were shown to be closer to the Mg end member dravite. The abundance of Mg and the lack of significant amounts of Fe are common to tourmaline crystals from both localities. In referencing a generic formula, the X site in these samples is occupied mostly by Na with trace amounts of Ca. The Y site is shown to be where the Mg exists with the little Fe available, and the Z site is composed almost entirely of Al. Another common feature amongst crystals from both localities is that they both exhibit void spaces that are interpreted to be from fluid inclusions when examined under the SEM. Further study is required to determine if the geochemical signatures in the tourmaline match those of other minerals from these pegmatites.