You are wrong, it's used everywhere throughout the Quran. What I think you might be asking about is why sometimes it's written as an "alef" without the "hamzah" like this: ( ا ) . The reason is in Arabic you have 2 kinds of "hamza", called همزة القطع hamzat al-qat' (the breaking hamzah) and همزة الوصل hamzat al-wasl (the connecting hamza) , The "breaking hamzah" is when the hamzah is pronounced clearly, cutting the flow of sound, this is when the hamzah is written above or under the alef depending on the vowel ( أ \ إ ) , the "connecting hamzah" is when the hamzah is not pronounced, allowing the sounds to connect together, and this type of hamzah is not written, only the Alef ( ا ) is written in this case, example: فارتقب يوم تأتى السماء بدخان مبين The word "تأتى" has a "breaking hamzah", it's pronounced (Ta' - ti ) , the hamzah sound creates a momentary stop in the middle of the word, it "breaks" the flow. But the word "فارتقب" has a "connecting hamza", so instead of pronouncing it like the first one ( Fa - 'Irtaqib ) , we connect the sounds ignoring the hamzah, so it is pronounced ( fartaqib ). This is the reason you will see the hamzah unwritten, it's because it's the "connecting hamzah".