During calcination of OCM catalyst precursors, Li ... Cs spectacularly lower the amorphous silica --> alpha-cristobalite phase transition temperature, shown here to be a critically important requirement for production of effective catalysts. Incorporation of W switches on OCM activity and newly discovered K/W and Rb/W formulations exhibit unsurpassed ethylene selectivity at high methane conversion. Addition of Mn significantly improves the performance of the former. An alkali-stabilised tungsten oxo species is thought to be the OCM active site.