This image is taken from a column experiment that mimics the Department of Energy's Hanford site in Washington state. At this site, highly caustic radioactive tank waste from plutonium processing has leaked into the subsurface causing dissolution of primary minerals and precipitation of secondary minerals, sodalite and cancrinite, which are capable of sequestering the radionuclides.
This column was packed with Hanford sand, then reacted with simulated tank waste. After the reaction, the column was sectioned and imaged using Scanning Electron Microscopy (SEM) Backscattered Electron (BSE) imaging. This particular image shows the inside of one of the sand grains where -- long before the experiment -- natural reactions precipitated minerals in an intricate layered pattern. The different shades of gray correspond to different minerals.