When a madd letter is followed by an original still consonant within the same word and the following consonant does not become doubled, the rule is madd lazim kalimi mukhaffaf. It is “kalimi” because it occurs inside a word and “mukhaffaf” because no doubled consonant follows.
«آلْآنَ» is the characteristic example. Its Qur’anic orthography and recitation involve a specific initial hamzah-and-madd sequence; one should not invent vowel marks from simplified spelling. The following original sukun creates the required prolongation.
This is not the same as madd muttasil. In muttasil, a following hamzah produces the added length; in this word, the decisive cause is original sukun. Remember both the structural cause and the absence of a doubled consonant.