The most common and most likely answer to this crossword clue is the 6 letter word FERRIC
I've seen this crossword clue in Financial Times
F
E
R
R
I
C
More clues leading to the result FERRIC
Buddy explains!
The straight part
We know that "of iron" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case of iron = ferric.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FERRIC mean?
FERRIC adjective- Pertaining to, derived from, or containing iron.
- Of compounds of iron in which it has a valence or oxidation number of 3