graphic granite core

Graphic granite (single scan)

Image of a 1" (25 mm) core of graphic granite. Light areas are potassium feldspar, and darker areas are quartz. Although these minerals have nearly identical densities, divergence in their x-ray attenuation behavior caused by their different atomic constituents allows them to be easily distinguished on a sub-millimeter scale. Optimizing the scanning and reconstruction conditions to bring out the division between these two phases causes micas and oxides to appear as pure white. (Sample provided by Dr. Robert Reed, University of Texas at Austin).