The most common and most likely answer to this crossword clue is the 4 letter word SARD
I've seen this crossword clue in The Daily Telegraph
S
A
R
D
Buddy explains!

The straight part
We know that "Stone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stone = sard.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 SARD mean?
SARD noun- A variety of carnelian, of a rich reddish yellow or brownish red color.
- Any of various brownish red earth pigments formerly used in cosmetics and painting; has more yellow, hardly any blue (see puce), is lighter than russet and darker than traditional carnelian.
- To have sexual intercourse with (a woman).