I am writing a science fiction novel where dead humans are turned into diamonds by compacting cremated remains. What size of diamond would the amount of carbon in a human body form? I know that the size would vary somewhat depending on the weight of the person.  

Specifically, would the diamond be small enough to be worn as an earring, or able to be worn as a necklace? Or would it be too large to practically be worn at all and be set as decoration?