The most common and most likely answer to this crossword clue is the 10 letter word KOH-I-NOOR
I've seen this crossword clue in The Guardian
K
O
H
-
I
-
N
O
O
R
More clues leading to the result KOH-I-NOOR
Buddy explains!

The straight part
We know that "large stone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case large stone = koh-i-noor.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.