Like some rock male member initially explained in exam (9)
I believe the answer is:
marmoreal
'like some rock' is the definition.
('marmoreal' means made of marble)
'male member initially explained in exam' is the wordplay.
'male' becomes 'm' (common abbreviation).
'member' becomes 'arm' (arm is a kind of member**).
'initially' indicates taking the first letters.
'in' is an insertion indicator.
'exam' becomes 'oral' (oral exam is a kind of exam).
The initial letter of 'explained' is 'e'.
'e' inserted within 'oral' is 'oreal'.
'm'+'arm'+'oreal'='MARMOREAL'
(Other definitions for marmoreal that I've seen before include "stony cold" , "made of stone" , "of fine stone" .)