Dengler, L.A. Effect of stress on the microstructure of a graywacke sandstone from the site of the Rio Blanco gas-stimulation experiment, report, September 30, 1975; (https://digital.library.unt.edu/ark:/67531/metadc868205/m1/1/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .