Man of stone (6)
I believe the answer is:
jasper
I believe this clue is a double definition.
'man' is the first definition.
(I have seen 'A man' mean 'jasper' so perhaps 'man' could also mean 'jasper')
'stone' is the second definition.
(I know that jasper is a type of opaque gem)
'of' acts as a link.
(Other definitions for jasper that I've seen before include "Semi-precious quartz stone -- boy's name" , "Opaque quartz" , "hard matter" , "A man" , "Reddish-brown stone used in jewellery" .)