Chocolate is a complex material consisting primarily of a finely crystallized continuous fatty lipid matrix (cocoa butter) in which cocoa powder and sugar particles are dispersed. With time, the lipid crystals tend to merge to form larger crystals on a micron scale, significantly effecting the texture and taste of the chocolate. These images are of an aged commercial dark chocolate sample. The topography of the surface is rendered in 3D, while the coloring is an overlay of the phase image, which highlights the compositional differences (darker patches being the growing cocoa butter crystals).
Image courtesy of Scott MacLaren, University of Illinois at Urbana-Champaign, USA