The non-vowelled noon (noon saakinah) ( النون الساكنة ): is the Noon which is void of a vowel. Its pronunciation depends on the letter following it. Nunnation (Tanween).
( التنوين ): This is the additional noon affixed to the end of the noun in pronunciation and in connected speech. The noun is void of the noon in writing and when a stop is made on it. Its symbol is two dhammahs (u), or two fatahas (a) or two kasrahs (i).
The Tajweed rules and the non-vowelled noon are equally applied to the non-vowelled noon resulting from nunnation (Tanween) N.B. When the non-vowelled noon and nunnation (Tanween) are followed by a conjunctive hamzah, neither of them is subjected to the rules of manifestation (Iz-haar) or assimilation (Idghaam), or turning (Iqlaab) or concealment (Ikhfaa').
Both of them are accompanied with a kasrah (i) vowel, in order to avoid the meeting of two non-vowelled letters (saakinayn).
An exception is the noon in ( من ) the possessive preposition (min) which takes the vowel fataha (a) not the kasrah (i) (to avoid the meeting of two non-vowelled letters; and also because of the heaviness in shifting from a kasrah (i) to fataha (a) It should be observed that the rule is applied to the non-vowelled noon (noon saakinah) and the nunnation (Tanween) only when they occur in the case of connected speech not in the case of stop.