Break small piece off end of thick raised surface (4)
I believe the answer is:
knap
'break small piece off' is the definition.
(knap can mean to break a piece of stone off)
'end of thick raised surface' is the wordplay.
'end of' suggests the final letters.
'raised surface' becomes 'nap' (raised threads on cloth).
The final letter of 'thick' is 'k'.
'k'+'nap'='KNAP'
(Other definitions for knap that I've seen before include "Rap" , "Strike stone" , "Deal hammer-blow" , "Break" , "Shape (a flint) by striking" .)