The schwa sound, represented by the symbol "ə", is a very common vowel sound in English, but it's not present in "iron".
Here's how the word "iron" is pronounced:
* I - the vowel sound in "it"
* r - the consonant sound "r"
* o - the vowel sound in "hot"
* n - the consonant sound "n"
Let me know if you'd like to know more about the schwa sound or any other phonetics concepts!