As some stones of course ground, grit's back (4-3)
I believe the answer is:
'as some stones of course ground grit's back' is the definition.
I can't judge whether this defines the answer.
'course ground grit's back' is the wordplay.
'ground' is an anagram indicator ('grind' the letters into a new form).
'back' says to take the final letters.
The last letter of 'grit' is 't'.
'course' is an anagram of 'rosecu'.
Can you help me to learn more?
(Other definitions for rose-cut that I've seen before include "Hemispherically-faceted style (of diamond)" , "(Of gem) finished with triangular faces" , "(Of a gem) having tiny triangular facets" .)