Piece of rock worth a number of pounds (5)
I believe the answer is:
stone
'piece of rock' is the definition.
(I've seen this before)
'worth a number of pounds' is the wordplay.
I cannot really see how this works, but
'a' could be 'one' and 'one' is found in the answer.
The remaining letters 'st' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stone that I've seen before include "Rock; gem" , "Olive pip" , "Rock; cherry seed" , "See 19" , "Imperial unit of weight" .)