THE MINERALOGY AND COMPOSITION OF THE CRYSTALS IN THE BENTONITE BED IN THE AUSTIN CHALK: OUTCROPPED AT TEN MILE CREEK (32°35'23.18”N, 96°48'54.00”W) LANCASTER, TX

A Cretaceous bentonite bed described in the Austin chalk outcropping at the WalMart section of Ten Mile Creek located east of Highway 35 in Lancaster, Dallas County, Texas, has predominant biotite crystals. The well-formed igneous crystals, such as biotite, suggest that this bed is of a different origin, compared to the other marine strata exposed at this location. Micas are not common mineralogy for sedimentary rocks, and biotite geochemistry specifically has been used to identify the volcanic origins of other bentonites during the Late Cretaceous. The minerals were identified by petrographic microscopy and can be verified using a scanning electron microscope with EDAX capabilities. The lose grain petrographic analysis of this bentonite yields numerous suhedral –anhedral biotite, anhedral altered quartz grains, with a very small amount of euhedral apatite. With the use of further analysis techniques such density separation, magnetic separation and x-ray defraction, to determine the biotite geochemistry in combination with whole rock chemistry and igneous mineralogy, there are possibilities of determining the volcanic source or correlating this bentonite bed with other known bentonites located in the North Texas Region, the Western Interior Seaway of the United States, or with the sub-marine volcanism occurring along the buried Paleozoic Ouachita structural belt in the Balcones in central to west Texas during the Late Cretaceous.