Periodic table extract showing elements commonly (green shading: B, Si, Ge, As, Sb, Te); irregularly (blue: Po, At); less commonly (pink: Se); and rarely (yellow: C, Al) recognised as metalloids. The staircase-shaped line between B and Al, Al and Si, Ge and As, Sb and Te, and Po and At is a typical example of the arbitrary metal–nonmetal dividing line found on some periodic tables.