THIN SECTION AND SCANNING ELECTRON MICROSCOPE STUDY OF INCLUSIONS IN TOPAZ FROM THE THOMAS RANGE, JUAB COUNTY, UTAH

The area of interest for this study is the Thomas Range, located in western Utah. The range trends north-south, is 12 miles long, and averages four to eight miles across. This locality is known for producing high quality samples, most prominently on Topaz Mountain. The collecting area is Topaz Valley and the east, north, and west slopes surrounding the valley on the south side of the mountain. The mineral of interest for the study, topaz, is found in abundance at this location. The topaz occurs in open gas pockets that are lined with tiny quartz crystals. The quartz grades to a granular rhyolite matrix. Topaz is found as clusters or single crystals, and may be doubly terminated. The topaz occurs along two sets of fractures in vugs along with hematite, pseudobrookite, bixbyite, quartz, calcite, fluorite, and a variety of other minerals. The focus of this research is the relationship between hematite and topaz.

The crystals of topaz occur from one extreme of inclusion free to the other extreme of full of inclusions. They are sherry-brown in color but become colorless when exposed to sunlight. All are found in the vugs of the rhyolite. A few main samples of interest have hematite growing out of the rhyolite at the base of the topaz and also on the crystal faces. Other samples of hematite are found inside the topaz crystals. Some of the hematite are found as free standing crystals and are not found in contact with topaz.

This research includes making three-dimensional cuts from the topaz rich vugs into the rhyolite. In order to do this the sample was cut in three directions; from these cuts thin sections have been made from multiple samples. Next the sections have been observed through a petrographic microscope to determine specific minerals that occur in the samples. Along with thin sections of the rhyolite, slides of individual topaz crystals from base to termination were made. The polished thin sections of rhyolite and crystals will be examined using a Scanning Electron Microscope (SEM). The outcome of the research will be the mineralogical sequence of growth, focusing mainly on the relationship between the hematite and topaz.