Fig. 3.5.

Different classes of icosahedra. The origin (H  =  0, K  =  0) in the equilateral triangular net represents the position of a fivefold vertex of an icosahedron, and the position of the neighboring fivefold vertex in that icosahedron is represented at a position (H, K) based on its T number (shown inside the circles). The icosahedra with K  =  0 (or H  =  0) belong to P  =  1 class (blue-filled circles). The icosahedra with H  =  K (on the dashed line) belong to P  =  3 class (green-filled circles). All other icosahedra belong to the skew class (open circles). These icosahedra exhibit lattices with handedness. Skewed icosahedra with H  >  K, below the dashed H  =  K line, are left-handed (laevo) lattices, and those with H  <  K, above the dashed line, are right-handed lattices (dextro)