Figure 2
From: Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite
“Dense” surfaces of silica polymorphs: (a,b) “Dense cristobalite”, side and top views; (c,d) “Dense surface” of quartz (001), side and top view; (e,f) “Shifted surface” of quartz (001), side and top views; (g,h) “Dense stishovite”, side and top views. Blue and red balls are silicon and oxygen atoms. Purple atoms are subsurface oxygens in stishovite. Each surface has four-coordinate Si and two-coordinate O-atoms on the top, and the surface layer can be described as a honeycomb made of corner-sharing SiO4-tetrahedra.
