Stone tool -- it goes into collapsed hole (6)
I believe the answer is:
eolith
'stone tool' is the definition.
(I've seen this before)
'it goes into collapsed hole' is the wordplay.
'goes into' indicates putting letters inside.
'collapsed' is an anagram indicator.
'hole' with letters rearranged gives 'eolh'.
'it' placed within 'eolh' is 'EOLITH'.
(Other definitions for eolith that I've seen before include "Elvis Presley song" , "Flint" , "stone tool" , "Old stone implement" , "Very early stone implement to be found in the oil" .)