In mineralogy , diamond ( from the ancient Greek αδάμας - adámas `` unbreakable '' ) is a metastable allotrope of carbon , where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice .
A diamond ( from the ancient Greek αδάμας - adámas `` unbreakable '' ) is a re-arrangement of carbon atoms ; those are also called allotropes .