"I am greedy for gems and rings."
Translation:Gemmas et anulos concupisco.
"I am greedy for" is not really a thing in the UK. If anything, it comes across as baby talk. You might just about get away with it if you are talking about food, but even there we would probably use a different construction, such as "He is greedy when it comes to food" or "He's mad about chips". In a figurative sense, those who are that way inclined "covet wealth", they are not "greedy for it". Even "desire", "crave", "long for" have to be better than "to be greedy for".