The combination [ŋŋ] arose exclusively as a result of [nɣ] > [ŋɣ] > [ŋŋ] and became [ŋg] (written “ng”) in Classical Adûnaic. Tolkien generally noted the full development from primitive to Classical Adûnaic as N3 > 93 > 99 > NG (SD/421,422), where “3” represented [ɣ], “9” represented [ŋ] and “NG” represented [ŋg]. This discussion here splits out the final stage of development into its own rule, since the earlier stages are special cases of the rules that [n] assimilated in position to following consonants and [ɣ] assimilated to preceding voiced consonants.