The most common and most likely answer to this crossword clue is the 10 letter word CONCHOIDAL
I've seen this crossword clue in Independent
C
O
N
C
H
O
I
D
A
L
Buddy explains!
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 CONCHOIDAL mean?
CONCHOIDAL adjective- Of or pertaining to a conchoid; that may be defined as a conchoid.
- (of a fracture) Irregular, with planar, concentric curves, similar to those on a mussel shell.
- (of a mineral) That fractures with planar concentric curves (e.g., as flint, chert or obsidian).