Open-File Report 20061366
U.S. GEOLOGICAL SURVEY
Open-File Report 2006-1366
By Joy Pochatila, Blair F. Jones, Kathryn M. Conko, and Daniel M. Webster
This study of mineral assemblages within the weathering profile at South Fork Brokenback Run, Shenandoah National Park, Virginia, extends previous research that focused on mass-balance calculations employing idealized formulation for the dissolution of primary mineral reactants in the granitic bedrock and for resulting mineral products in the overlying saprolite. From two cores of the granite weathering profile (regolith) obtained in an earlier investigation, mineralogical and chemical analyses of five physically separated fractions of the saprolite were obtained for discrete depth increments. X-ray diffraction (XRD) analyses identified quartz, potassium feldspar, biotite, amphibole, plagioclase, illite, kaolinite, and goethite, in addition to a 2:1 expandable clay, considered an aluminous smectite. CLAYFORM, a computer program for calculating structural formulae of clay minerals from elemental chemical analyses, was used to characterize the composition of the finest fractions containing the most smectite, which appeared to range from K0.4(Si3.0Al1.0)4.0(Al2.0Mg0.3)2.33O10(OH)2toCa0.3(Si3.0Al1.0)4.0(Al2.0Mg0.2)2.33O10(OH)2. This clay was taken to be an important intermediate in the weathering of the granite.
Mineral Separation Technique
X-ray Diffraction Procedures
Estimating Mineral Abundance
Use of CLAYFORM to develop a clay-mineral Formula
Mineralogical and Chemical Composition of Saprolite
This report is available online in Portable Document Format (PDF). If you do not have the Adobe PDF Reader, it is available for free download from Adobe Systems Incorporated.
Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Adobe Reader 8.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.
|AccessibilityFOIAPrivacyPolicies and Notices|
|U.S. Department of the Interior, U.S. Geological Survey
Page Contact Information: Contact USGS
Last modified: Saturday, January 12 2013, 10:35:55 PM