Help up rocker's foe cut by head of nasty Stone (7)
I believe the answer is:
diamond
'stone' is the definition.
(I know that diamond is a type of transparent gem)
'help up rocker's foe cut by head of nasty' is the wordplay.
'help' becomes 'maid' (help can mean servants).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'rocker's foe' becomes 'od' (I can't explain this - if you can you should give a lot more credence to this answer).
'cut by' indicates putting letters inside (some letters cut into others).
'head of' suggests taking the first letters.
The first letter of 'nasty' is 'n'.
'maid' written backwards gives 'diam'.
'od' enclosing 'n' is 'ond'.
'diam'+'ond'='DIAMOND'
Can you help me to learn more?
(Other definitions for diamond that I've seen before include "(Usually colourless) gemstone - card" , "Gem stone" , "The hard stuff" , "Playing card - baseball playing-field" , "one of thirteen?" .)