Among miners, daughter is revealing practice (6)
I believe the answer is:
nudism
'revealing practice' is the definition.
(nudists reveal their naked bodies)
'among miners daughter is' is the wordplay.
'among' is an insertion indicator (inserted letters are placed among others).
'miners' becomes 'NUM' (National Union of Mineworkers).
'daughter' becomes 'd' (genealogical abbreviation).
'd'+'is'='dis'
'num' enclosing 'dis' is 'NUDISM'.
(Other definitions for nudism that I've seen before include "Practice of going naked" , "Going without clothes, socially" , "Practice of living as nature intended" , "Practice of going without clothes" , "The practice of wearing no clothes" .)