The most common and most likely answer to this crossword clue is the 10 letter word TRAVERTINE
T
R
A
V
E
R
T
I
N
E
Buddy explains!
The straight part
We know that "limestone deposit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case limestone deposit = travertine.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 TRAVERTINE mean?
TRAVERTINE noun- A light, porous form of concretionary limestone (or calcite) deposited from solution, and sometimes quarried for building.