The most common and most likely answer to this crossword clue is the 9 letter word ALLOTROPE
I've seen this crossword clue in The Times
A
L
L
O
T
R
O
P
E
More clues leading to the result ALLOTROPE
Buddy explains!
The straight part
We know that "an element in a different form" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an element in a different form = allotrope.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 ALLOTROPE mean?
ALLOTROPE noun- Any form of an element that has a distinctly different molecular structure to another form of the same element.