Prince, Prince, Prince — just the ultimate type of rock (5)
'prince' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for jewel that I've seen before include "Gemstone" , "(Semi) precious stone" , "eg Ruby" , "The - That Was Ours (Dexter)" , "Precious stone or mineral" .)
'rock' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Another definition for prase that I've seen is " quartz".)