The most common and most likely answer to this crossword clue is the 4 plus 5 letter word RARE EARTH
I've seen this crossword clue in Financial Times
R
A
R
E
E
A
R
T
H
More clues leading to the result RARE EARTH
- Rather agitated, holding live element
- Thin soil yielding metallic element
- Unusual soil element in each half of divided land?
- Blue Planet’s unusual element?
- Energy lost from dodgy rear heater’s element
- Table item army groups found beside Globe
- Element of Blue Planet?
- Element that’s literally thin on the ground!
- Element scarce on planet
- Metallic element radium and three rocks containing argon
Buddy explains!
The straight part
We know that "unusual element" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unusual element = rare earth.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.